First Light with new ASI585MC Pro.: Page 7

First Light with new ASI585MC Pro.

Kevin_A

w7ay my 52mm filter ring turned off really easy… like it was just hand tightened! Haha

w7ay

Kevin_A like it was just hand tightened!

Must be a Tiffen. That is why I prefer them to use as a glassless filter :-)

Remember I was going to use an Astronomik L1 as a UV/IR cut "prefilter?" I.e., pass light through it first before the actual narrowband OIII filter, for example.

Well, I found a nice QHY 54mm spacer (QHY-020076 -- Cyclops Optics claim 13.5mm mechanical length; no useful info at Highpoint, as usual) that is internally threaded to take a 2" filter. The Astronomik is 1mm glass, so the optical length is 13.8mm (I will measure the mechanical distance more carefully once I have one on hand). When used with a ZWO filter drawer and ASI2600MC backfocus, I need an extra 3mm or so to get the Takahashi 56.2mm backfocus to work out. (A 55mm backfocus OTA might not even need a shim- just M54 OTA, QHY spacer (with an internal 2" filter), ZWO filter drawer (or EFW) and the 17.5mm flange of the camera) So, this may be a decent solution to stack filters, or even use as a primary filter holder in place of a ZWO filter drawer (less potential tilt). I just bought the last two in stock at HighPoint, but Telescopes Canada in your end of the wood, has them https://telescopescanada.ca/products/qhyccd-m54-male-to-m54-female-adapter-020076 :-.)

Chen

w7ay

Kevin_A I chose the Esprit… no diagrams…. just very good testimonials.

You are a much braver person than I am.

Askar (and even their cheaper SharpStars) is very good in this aspect. Takahashi scopes are well documented. Old fashioned manufacturing company. NHK video, so in Japanese:; but can apply English as Close Caption https://www.youtube.com/watch?v=hnkwDLFdVX4 .

Watch their collimation some 10 minutes into the video. Wonder how much time the Chinese companies spend on collimation.

Chen

Kevin_A

w7ay the Takahashi workers are almost as meticulous as I am! Haha
Seriously, almost!
I don’t have any problem tearing something new apart right away if I can improve it or if I see a speck of dust.
I have already had my Esprit apart and no more saggy dewshield which is well known to be an issue. It is a very well built scope as well. It has a dual rail drawtube which I find nice and a very nice and big 3.4” focusser. It is very short, has a rolled steel drawtube and it is a heavy 16.5 lbs empty. Built like a tank! No aluminum here but lots of nice baffles. Can you tell that I do not like loose cables… OCD!

Kevin_A

w7ay the Esprit has been called a poor man’s Tak! Haha It is almost as good but 1/3rd the price! When I say it is a beast… it is! The scopes tube ring diameter is 130mm and it’s only a 100mm objective. Well built and long cooldown too.

w7ay

Kevin_A It is very short, has a rolled steel drawtube and it is a heavy 16.5 lbs empty.

Ouch. That is heavier than the naked FSQ-106 (15.4 lbs). The 15.4 lbs ihas been what is causing me from ordering one (takes usually 9 mo to a year wait for a production run). 16.5 lbs? Fuggetaboutit.

Chen

Kevin_A

w7ay that’s what I was hesitant about, but compared to my 115mm triplet that is light at 12.2lbs naked weight, it is easier because it is so short and the weight is localized better. The lens cell is right at the back of the huge long dew shield. The other quirky thing is that once you have the rings on you cannot retract the shield more than 1.5in! Weird. I thought I was imaging tonight but it is a head fake… clouds are coming as soon as dusk hits! Typical for my region!

w7ay

Kevin_A it is easier because it is so short and the weight is localized better.

Hah! Wait until you add a loaded EFW :-). Those things are really heavy once you add glass -- especially the 3mm thick Chroma and Astrodon ones.

It is so bad that I have split my 2" filters into two different EFW. One has LRGB and the other has SH(alpha)OH(beta).

My 36mm EFW is loaded with LRGBSHO (no H beta). All 3mm thick Chroma glass. Weighs a bloody ton.

That is why I am thinking of when not doing narrowband, using the mono camera just for L (thus just a simple 2" drawer, or that QHY M54 spacer that has 2" filter thread), with a Bayer camera for RGB (with the same L filter in front of it). I am not getting younger and have to start worrying about even the existing weight. Soon, I will be back to the Borgs again (really light but strong).

The FSQ-85 is tiny, until you extend it with tubes for flattener, EFW and camera, and extend the dew shield. By the time you are done, the length is more than doubled (and not as cute).

But not half as bad as the FOA60Q that is set up with a solar etalon and rear ERF (notice guide scope replaced by the Hinode Solar guider, that is no longer needed with the "e" RST135):

Chen

Kevin_A

Nice array of Taks! Maybe one day I will get one!
Till then… close will be good enough! Haha
Cheers!

w7ay

Kevin_A Till then… close will be good enough!

The FOA60Q has the highest Stehl ratio (0.998, and with humans actually QA it, as the NHK YouTube video shows :-) for consumer telescopes. Even Takahashi says it wipes the floor with the rest of Takahashis (FSQ-85 has Strehl ratio 0.975). Nothing will come close to FOA-60Q; it is Takahashi's tour de force :-). The Askar 151PHQ has a Strehl of 0.97 for example.

I don't really need good chromatic Stehl for the narrowband Solar work (even a singlet is good enough for Solar etalon type bandwidths), but I just wanted to own the sharpest telescope on earth (at least for consumers :-), and actually quite cheap to do so. Heck, seeing here is bad enough, I doubt I ever need Strehl better than 0.95.

For its lower Strehl ratio, the FSQ-85 Baby-Q star shapes and sizes are not too bad though. The real FSQ (FSQ106) has a Strehl of 0.98 (http://interferometrie.blogspot.com/2016/04/106530-takahashi-fsq-nr2.html ).

Chen

Kevin_A

w7ay here is a back to back comparison of the 52mm aperture ring vs f2.8 blades and another at f2.4 which I will test with the 52mm in place to see the blades being slightly in the optical pass has any effects on the star diffraction patterns.

52mm ring, lens wide open

Lens at f2.8

Lens at f2.4

w7ay

Kevin_A h

Kevin,

Here are some tests; clouds cleared at sunset, although rains are back tomorrow evening.

I placed Alioth (M+1.75) at a corner of an APS-C frame (ASI6200MC using the APS-C ROI) and refocused (I still need to tune the backfocus, so I am refocusing the corner -- the ASIAIR "autofocus" can't handle this kind of focusing :-).

BTW, the 3-D printed Bahtinov I used really sucks. Notice the broad and wiggly central diffraction spikes near the star. I am going to try mounting my glass SharpStar Bahtinov mask on the Rokinon's lens hood (no, not the Chinese Sharpstar, but a US company called Lonely Speck).

For the FSQ-85, I had mounted the SharpStar (looks like a 100mm x 100mm square filter that professional photographers use) to a Thousand Oaks aluminum cell, with the polymer filter material removed (:-), plus a number of step-up and step-down camera rings.

https://www.lonelyspeck.com/sharpstar/

Anyhow... a 52mm Tiffen (47mm clear aperture, or about f/2.9 135mm lens) gives the following 5 seconds exposure (way saturated) for Alioth at the bottom left corner (Magnitude +1.76, so just a little brighter than Alnitak for Horsehead. At f/2.8, Horsehead probably can take 30 second exposures with gain 100.

A 55mm Tiffen (f/2.7 at 135mm) will be better, in terms of the notched diffraction pattern. 55mm will probably be what I will use the Rokinon at for APS-C cameras (since it is basically a 50mm astrograph).

It looks from the above like the other lens aberrations are already greater than the notch. The lens is still not shabby though, at f/2.9. I can live with it. Better than the other 50mm to 180mm lenses/OTA that I have tried, so I am pretty happy (irrespective to the price of the Rokinon). Now that I am hooked on 135mm, I may take a look at Zeiss' Milvus 135/2.0 one day, ha ha.

Here is the above zoomed (you can judge the zoom factor from the red target circle). See the two aperture vignetting notches? But the star itself is no longer round from other lens aberrations anyway (even though I focused on it). Other dimmer stars look fine, even under this magnification (why I am happy enough with this lens; even Sigma ARTs don't come close to this kind of performance at the corners of an APS-C frame). The notches is very low level, and requres very saturated stars with a large point spread function skirt.

Stars nearer the center won't be apearture vignetted, of course.

Chen

w7ay

@Kevin_A

Kevin, these two might also work to add a 2" filter to an M54 imaging train (e.g., have an additional filter to stack a filter drawer or EFW). I think it has an internal M48 filter thread, if it is like some of ZWO's adapters:

https://astronomy-imaging-camera.com/product/m54-m54-16-5-adapter/
https://astronomy-imaging-camera.com/product/m54-m54-21-adapter/

16.5 mm thick and 21mm thick vs the QHY one that is 13.5 mm thick.

Chen

Kevin_A

w7ay I managed to get 60 x 60s shots at gain 100 last night and will be posting soon. I might swap my lens out soon as it is showing signs of longitudinal aberrations as my bright stars are showing more red fringing these days. Not sure why or how it happened… maybe a lens shifted after 8 years owning it. Someone told me that they are glued in place. It too noticed the starfish stars at the edges on mine. Those clear etched masks are not good from what I have heard and I just ordered a fine pitch one yesterday on Etsy from Astrodymium… same maker as the lens holder ring setup.

w7ay

Kevin_A is showing signs of longitudinal aberrations as my bright stars are showing more red fringing these days

Did you stop using real (not the cheap ZWO stuff) UV-IR filters in front of your ASI2600MC?

I will have some measurements coming up in the next couple of days. For the ASI2600MC, I used a "D60 IR-CUT window." It will probably explain both the blue fringe (for OTAs that bloats the UV below 400nm) and the red fringe. The 2" ZWO "UV-IR Cut" filter isn't measurably better. As with other ZWO stuff, you will have to buy something better later to replace their products (even their own, viz, 3 versions of their filter holders so far, they just make you throw the old useless ones away and pay them again for the new one -- I assume you have the new EOS adapter with filter drawer, right?).

I just ordered a fine pitch one yesterday on Etsy from Astrodymium…

That is the one I used that produces the wiggly stuff near the star :-). You may have better luck. The edges of 3D printed stuff is really rough when it comes to optical wavelenths.

Now, the WO clear plastic ones are equally crummy: the thick plastic produces too much color dispersion, and I could never get very precise focus from them: red, green and blue all mushed together. The Lonely Speck one is thin glass.

So far, the only thing that I am unhappy with the Rokinon is when you have to rotate the camera angle. The ZWO EOS adapter does not support rotation, so the only way is to remove the belt. I am right mow investigating using the SmallRig "Follow-focus" pinion gears that can be more easily "declutched." The Rokinon Cine comes with integral M0.8 ring gears (one of the reasons I chose it instead of the photo version).

The difraction spikes are x4 now.

x4? Is that a millennial slang? 4 times larger? (I don't see the 18 pointed spikes, though) Never heard of it. But I don't even own a smart phone even though some of the algorithms I worked on are in the iPhone today (heck, how I could retire moderately comfortably :-); I am still using a flip phone :-).

Chen

Kevin_A

Well, flats are not working well for me but here is 1 hour with the lens wide open and with the 52mm stepdown. 60s shots at gain 100 on 2600mc pro. The difraction spikes are x4 now.

Kevin_A

w7ay I use a Svbony uvir cut filter in front of the 2600. Not sure how it compares. I hear you about the need to move the lens and remove the belt… a pain. The 4X difraction spike is as shown on bright stars… not slang.

I use a Samsung Galaxy S10…. A few behind the S24

w7ay

Kevin_A The 4X difraction spike is as shown on bright stars… not slang.

The notches probably comes from an aperture vignetting in both x and not-x directions. I see two strong (180º spaced) notches and two weaker notches at a different angle (not orthogonal, either, to the first set).

Is this at a corner of a frame? If so, move the star to the middle of the edge instead of corner -- does the four-fold diffraction notches become a two-fold notch?

Chen

w7ay

Kevin_A I use a Samsung Galaxy S10…. A few behind the S24

I do use an iPad to take quick and dirty pictures (like the ones I post here).

Chen

w7ay

Kevin_A I hear you about the need to move the lens and remove the belt… a pain.

Especially when shimming the backfocus. The shims changes the camera angle, a real pain when trying to position a bright star at the corner.

I might be able to do the backfocus indoors using an artificial star, since the focal length is much shorter than traditional OTA. Might at least be able to get close if I can pivot the camera right at the plane of the sensor. Stable air indoors makes it easy to see Airy rings too, and I have in the past been able to get Bahtinov spikes indoors.

Still... change shim, and image rotates! Indoors or outdoors. Each time I change shim, I need to move an artificial star to the optical axis and then to the corner of the frame. If the field is not flat, the two positions will yield different focus positions. Thank heavens for electronic focusers :-).

Chen

w7ay

Kevin_A I hear you about the need to move the lens and remove the belt… a pain.

OK, quick test...

Eppur si movre :-).

http://www.w7ay.net/site/Images/Rokinon%20M0.8%2038T.mov

The Rokinon Cine comes with the 0.8 MOD ring gear (for both focuser and aperture control). Here you can see the EAF driving a standard M0.8 38T pinion gear.

The EAF is mounted to one of the Astrodymium rings (some unused old plates I'd made up for various OTAs); a quick hack. Once I test enough to know that it works resonably well, I will have a rod from the gear all the way to the front Astrodymium ring to a flange bearing -- that will give it a more solid attachment.

With the particular angle the EAF is mounted on the Astrodymium ring, when the ring is completely loosened, the gear lifts from the focus ring, and the lens is now free to rotate (if the second Astrodymium ring is slightly loosened).

I should also be able to "hinge" the EAF plate (nice to have a web machine shop nearby :-), so that it can be lifted without even lossening any of the Astrodymium rings. This will allow fast manual focus and also allow the Astrodymium to be just loose enough to change camera angle.

OK, problem over... no more tearing hair out in the dark trying to reattach belts. Or when adjusting shims for backfocus.

By the way, you can get rubber follow-focus M0.8 ring gears that fits over regular lenses, so you can play this trick with the non-Cine verion of the Samyang, too.

https://tilta.com/shop/seamless-focus-gear-ring/

Chen

Kevin_A

w7ay that star was at the edge.

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