First Light with new ASI585MC Pro.: Page 14

First Light with new ASI585MC Pro.

Kevin_A

w7ay there are a few companies that have a metal M42 adapter that replaces the eos mount. There may be a m48 available too… you just have to look around. Here is just an example.

https://ensoptical.co.uk/index.php?route=product/product&product_id=13220

w7ay

Kevin_A https://ensoptical.co.uk/index.php?route=product/product&product_id=13220

Yeah, the M42 one is way too small an opening. Typically, the clear aperture of a male M42 thread is around 38mm. That's 5mm away from the corners of an APS-C frame. If the lens is f/4, placing an M42 thread just 20mm away from the sensor would produce aperture vignetting (the kind that give you notches in the halo/aura of a lens). Faster lens is worse, of course. Not good, even on paper. That is also why I replaced the 36mm LRGBSHO filter wheel with a 2" set.

M48 is much better (and 2" filters typically don't have a 48mm clear aperture anyway), and the store does have a M48 version for the Samyang 135mm.

https://ensoptical.co.uk/index.php?route=product/product&product_id=13221

But their specs are a little confusing, mentioning an M42 thread's thread height. I assume (making an ass of u and me) the M48 one is the same, and they simply suffer the ZWO "copy-and-paste" disease.

Since it is M48, there is no internal thread for a 2" filter. But their 44mm backfocus (same as EF lens' flange focal distance) gives 44mm-17.5mm (camera flange)-13.5mm (Blue Fireball CAA) gives 13mm to spare for shimming, plus an extra M54 spacer that can take a 2" filter. Should be a moderate breeze to get correct spacer for backfocus with that much to spare.

Thanks for the link -- I just ordered one of the M48 ones for the Rikonon, and one for the Samyang. This will bypass all flakey ZWO stuff in between the camera and the lens. I try to avoid any ZWO stuff that is in the light path between the sky and the sensor :-)

PayPal is doing the currency conversion thievery :-).

Chen

w7ay

Kevin, all this playing with fast short focal length lenses is getting me interested in wide FOV again.

The FSQ-85 with the 0.73x reducer gets it to 327mm focal length, but is not really good for beyond APS-C sized sensors. Even for APS-C, it is definitely nowhere close to what I can get from the FSQ with just the 1.01x flattener; so I don't use the reducer often (I like pinpoint stars).

Unlike the other Askars, the FRA300 is sort of OK, actually. At least my copy. Take a look at the corner stars on an ASI2600 sensor:

http://www.w7ay.net/site/Images/NGC7000-FR300-Lult.png

The stars at all four APS-C corners are kinda usable -- a bit bloated, but very little coma. Askar's own published spot diagram shows an Airy disk at the APS-C corner that is about twice the radius as the disk at the center, and the bloat shows it.

So, call me crazy, but I have been looking at the WO Pleiades 68, which is a fast f/3.8. Heck, if I were to stop down the Rikonon to an F/4, the WO scope is even faster, and with a focal length of 260mm, i.e., twice the Rikonon's focal length, and not much longer than half of the focal length of the FSQ85 with flattener.

I don't use the FRA300 much because it is so slow. But I do resort to using it when I need a shorter focal length than the Baby-Q. The small Pleiades would have solved the (lack of) speed issue.

The problem is that I have been bitten once by WO a few years ago with a WhiteCat51 that has a tilt (first gen, so it did not come with a tilt plate) -- apparently , so many people have the same problem, the second gen RedCat came with a tilt adjuster :-). Don't know if I can trust them.

Bat a fast 260mm sure is tempting, and WO does publish spot diagrams for it. RMS Airy radius is just about 2 µm, so pretty much same spot sizes as the FRA300, and all the way to the corner. So, not quite Japanese image quality. The Pleiades is not a Petzval, so require good backfocus, but I know how to handle backfocus now :-).

Camera lenses are fun, but I still prefer an astrograph that is designed just for infinity focus. If only WO didn't lose my trust with the crummy Cat51.

Chen

Kevin_A

w7ay do-not get the WO68… lots of reported problems with backfocus and tilt and coma. I have had problems with their scopes… returned two and sold next one fast.

Kevin_A

w7ay I only like my Fra300 slightly….. mainly because it is not wide enough or big enough nor fast enough. No wow factor! If it were f4 or faster then I might like it more. Right now it just does not offer a wow factor big enough for me to use a 60mm objective due to low object signal.

w7ay

Kevin_A lots of reported problems with backfocus and tilt and coma

Yep, you would expect that from an f/3.8.

The scope comes with an internal tilt adjuster, and backfocus is a problem only for those who don't know what a flat field actually means -- the unwashed use the "radial-stars vs circumferential-stars" hobbyists rule of thumb, which is highly inaccurate. Just use the definition of the flatness of the image plane, and the problem is manageable.

I read a Cloudy NIght thread on the Plieades 68, and the OP complained about coma, when he didn't even set the correct backfocus! WO's web page has copious warnings that this sope (vs the Cat71) is not meant for novices. Click on "Which Telescope to choose -- Plieades 68 or Cat71 WIFO." Read between the lines, and they try hard to not use insulting words for the Cat71's target customers :-)

https://williamoptics.com/products/pleiades-68

I don't even believe their "exact 55mm" backfocus claim. I'll bet they build these in China, and you get Chinese QA. But that is easily measured -- just need a high resolution Bahtinov mask, not their rough plexiglass one. All the free WO Bahtinov masks are worth exactly what you paid for them.

I'll pull the trigger and spend some time tuning it as a project. If the optics is OK, the mechanical issues are not insurmountable. The 260mm at f/3.8 is just too tempting. (I may have to aperture mask it down to a 60mm/f4.5, though; we shall see.)

I downloaded their documentation, and unlike ZWO, is quite detailed. Publishing spot diagrams in the User Manual is a good sign that they care.

I have had problems with their scopes… returned two and sold next one fast.

Yep, my experience with the first generation Cat51 (mine is white), too. Optical quality is very good, but has a bad tilt. And I have been avoiding WO like the plaque until now.

From the spot diagrams, this is obviously not even close to a Tak, but pretty similar to spot diagrams from the better Askars. Notice that they don't cheat like Askar either. Tak and this WO uses a 100µm x 100µm spot diagram, while Askar uses 200µm x 200µm to make it appear to be better :-). Unfortunately, Tak don't make short focal length Astrographs -- I would buy one sight unseen.

Chen

w7ay

Kevin_A I only like my Fra300 slightly….. mainly because it is not wide enough or big enough nor fast enough. No wow factor!

That is why the WO's f/3.8 got my attention. (Wow!)

The thing about my FRA300 is that there is nothing wrong with it. Darn thing is very well behaved. Just that at f/5, it is too slow to waste time imaging.

Same with all the Askars that ZWO sells -- too darn slow to enjoy as an astrograph. Their 65mm one has a smaller aperture than the Pleiades 68, but a whopping 416mm focal length. An astrograph with f/6.4??! You need to spend 65% more time to capture the same amount of photons as the WO. It is even slower than the FRA300. Also, notice that the central spot size for the ZWO 65mm is touted to be 2.5µm (typical of the lower grade Askars), while the Pleiades 68 and FRA300 both come in at a little under 2.0µm.

But wait, it gets worse from there... ZWO's 107mm Askar is even slower, at f/7, their 85mm Askar is f/7.5, And the 130mm one clocks in at f/7.7! Zzzzzzz.... The stars for the 130 will be very bright (big aperture) but the nebulas will be very dim (slow f-number). The saturated stars will appear very bloated by the time you integrate for long enough to see the nebula :-).

Chen

Kevin_A

w7ay I also wonder if the cine version of the Rokinon 135 would have less backlash in the focus mechanism vs the standard version since a cine version is expected to go back n forth more often due to the nature of its intent and intended inclusion of using a focussing gear. My regular version has a tiny bit of backlash and that will affect my eaf unless I manually focus in one direction.

w7ay

Kevin_A My regular version has a tiny bit of backlash and that will affect my eaf unless I manually focus in one direction.

Well, the ZWO electronic focuser has enough backlash that you need to do this (focus only in one direction) anyway.

Chen

Kevin_A

w7ay unfortunately I cannot convert my lens due to the electronic aperture on my Nikon version.

w7ay

Kevin_A unfortunately I cannot convert my lens due to the electronic aperture on my Nikon version.

Darn... time to move to EF mount?

The thing about my EF mount manual lenses is that I have yet need to hook them up to a real camera, So, it is moderately safe to move to an EF mount, even if you don't have a Canon camera. I still have some 5D's (up to Mk III) from before the time I moved to using the Sony A7 stuff, so I do have Canon cameras available if I need them.

Now, I do not own Nikon (ever since the Coolpix in the 1970s, and back when I was a teenager, with my Dad's Nikon SP). So, if the iris of the Sigma 40 ever closes on me, I would need to go find a cheap refurbished Nikon camera.

By the way, I have only played with the Sigma 40 a few times (trying to see how to attach an EAF, etc) and the left handed thread of its bayonet has already fooled me more than once.

Chen

Kevin_A

w7ay yes, I have no patience to spend 15 hours on a target. Tooo slow! I also start imaging at 10pm this time of year and I will not leave my scope out overnight due to crazy weather changes so I image to 2am max, so I am too old to stay up past that so 4 hours a night is the very max…. So fast is my friend, so is light for most of my imaging sessions!

Kevin_A

w7ay my cameras and lenses are all nikon so I can’t switch now unfortunately.

w7ay

Kevin_A yes, I have no patience to spend 15 hours on a target. Tooo slow!

With all the trees around me, I am lucky to get 3 hours per night on any target. More time towards the north, above 60º declination. The south is hopeless because of lights from Portland metro and Beaverton.

Fast is not just fun. It is a neccessity.

Chen

Kevin_A

w7ay I was thinking about the 68 but was scared from my last WO scope. My first one had coma, elongation and tilt in opposite areas. My replacement had pinched optics. I fixed that but sold it right away. I do like their glass choices as the colours were very rich! 7 elements is a whole lot to keep perfectly aligned. I know backfocus was an issue that some could not fix for whatever reasons but coma is not something easily fixed.

w7ay

Kevin_A but coma is not something easily fixed.

Yep, if there is coma, the scope goes into the trash. But a lot of "coma problem" is simply caused by bad backfocus. Like this one:

https://www.cloudynights.com/topic/904695-wo68-pleiades-first-light-report/

Nothing is ever as bad as the first image. In the very first sentence, he even thinks it is a Petzval, which it for sure isn't. The backfocus has to be precise with this scope, and I don't believe their "exactly 55mm" claim either.

Well, I pulled the trigger, so we will see. I have stayed away from WO ever since the first generation Cat51. The 68 is just too tempting not to give them another chance.

Remember I bought couple more of the Askar backfocus adjusters from that Alberta (All-Star) store? Well, one is destined to be be mounted permanently on the WO. At f/3.8, that thing probably needs 100-microns type backfocus accuracy!

Chen

w7ay

Kevin_A

Hah, in another thread, someone was asking for ASIAIR to support changing EAF steps based on filters (presumably filter thicknesses).

If you remember a couple of posts back on this thread, I had mentioned that for non-Petzval scopes, you don't want to change the focus (distance between the OTA glass and the flattener/reducer), and actually only need to change the backfocus between the flattener/reducer and the camera flange, the optical path where the filter drawer/filter wheel resides.

Again, hobbyists understanding of filters don't jive with math and Physics. (Think the YouTube shills will understand this difference even when you point it out to them?)

No, the Antlia backfocus adjuster is probably too stiff to connect an EAF to :-).

You can get the correct adjustment by using two back-to-back electronic filter wheels. One filter wheel has your regular filters, and the second filter wheel has clear glass with different thicknesses. Mix and match to get a constant total glass thickness. But I am not sure I like adding glass to the optical path after my experiment with a prefilter for a narrowband filter.

That said, I should look into adding a filter wheel before the FSQ flattener. That then will allow just refocusing to work, no need to play with back focus. Problem is that thread is an M72. Even the Antlia filter drawer will only handle M68. Perhaps Baader has one.

Chen

Kevin_A

w7ay I find that most people do not understand the very basics. Another reason I stayed away from WO was that I discovered and posted about a design flaw in their variable reducer flatteners. They machined a flat thru all the threads where they put the incremental markings and unfortunately that flat allowed light right thru inside the flattener. I contacted them but they were not responsive and it was easily fixed by just not machining thru the last few threads. I told people that the only easy solution for them was a few wraps of electrical tape to block the light leak.

w7ay

I wrote: Perhaps Baader has one.

Indeed they do. Their Universal Filter Drawer has these adapters for the telescope end (right hand side of the screenshot):

Or use these to go from the Takahashi's M72 to a M54 filter wheel/filter drawer:

https://agenaastro.com/blue-fireball-m72-male-to-m54-male-thread-adapter-for-takahashi-fsq106-m-26.html
https://agenaastro.com/pegasus-astro-m72x1-takahashi-to-m54x0-75-male-thread-adapter-peg-adapt-m72m-m54m.html

But I also need to get back to M72 again to attach the flattener :-). PreciseParts can always make one.

Next is to look at the light rays to see if a 2" filter is big enough.

P.S., no problem, the flattener glass itself is only a little more than 40mm.

Now, here is the interesting thing... this is also a good place to install a OAG, but will need one with a long reach to the guide camera sensor.

Chen

w7ay

Kevin_A I discovered and posted about a design flaw in their variable reducer flatteners.

I never like the one size fits all flatteners. I tolerate them for guide scopes, but for something I want to waste valuable time imaging with, I rather pay more for flatteners optically designed for that particular scope. The one size fits all reducers and flatteners just model a "typical" doublet or triplet at a given focal length. You then change its position in the optical path (usually a screw type motion) to try to match other different focal lengths.

Penny wise, pound foolish. Waste of money on the long run, since one day you will end up not being happy with it and pay again for something that works properly.

They machined a flat thru all the threads where they put the incremental markings and unfortunately that flat allowed light right thru inside the flattener.

You wonder if these idiots ever have staff that knows how to use their own products. I know that as of 2 or three years ago, no one at ZWO did astrophotography except for Sam himself, and Sam mostly did planetary with bright targets. That could account for light leaks in ZWO products left and right (they still haven't fixed the leak around the stepper motor of all the EFW). Eventually, especially during the pandemic, I know a couple of them started to play with telescopes after joining ZWO. Anyone asking ZWO technical questions on this forum is asking the blind to lead the blind -- you are asking someone with next to zero technical knowledge. When they started building the ASIAIR, no one at ZWO knew spherical geometry (the old Greek geometry of latitude and longitudes, which is different from the Euclidean [existence of parallel lines] x-y coordinates that we call "geometry" today). That is why they have no idea how to properly meridian flip, nor even know what Local Sidereal Time is.

Don't believe me? Just ask them on this forum how one computes Local Sidereal time. Their concept of astronomical time actually includes Daylight Saving Time!

Chen

Kevin_A

w7ay that was one reason I went with an old school Esprit 100ED as the flattener was specifically designed for it only. In reality most of their engineering and technical side is farmed out. My Astrodymium rings will arrive today, I had him add an extra 80mm holder upright in with my order so I can play around with how I am going to hold my SP35 f1.4 lens. Yaaaa! Haha

Kevin_A

w7ay yes they are definitely not experts in some fields… just makes me think of the latest offering… asi2600mc duo Air! WTF? Haha

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