w7ay I got my ring setup. It does not look like I can get my EAF to work right now as I will have to modify a few things. The gear ring is too small and the holder interferes etc. I have an extra 80mm bore upright but that too is problematic in holding the lens. The current 70mm rear upright is a perfect fit for the Nikon adapter so my focus ring is in front for now.
Lots to think about!
w7ay it is fairly neat when you consider the 2 dew heaters. They always add lots of cabling on small setups. I want to first see how it performs before going much further. Even in a Bortle 4 I still get massive gradients from low light pollution. It may be a rig I only use in a darker area like near the lake.
Hah, looks like WO made an error with the backfocus. It is really around 57.5mm (see Agena page on the Pleiades 68), and people have been using the 55mm (remember I didn't believe that number?) and complaining about coma.
Definitely proves that no one at that company even test their products under the night sky.
They are simply issuing new spacers to reduce the backfocus to 55mm. But, heck, I am sticking with the original spacers to get an extra 2.5mm of backfocus to play with. Or get PreciseParts to make me a spacer to get 56.2mm backfocus to match the FSQ stuff.
I suspect the Pleiades 68 that is coming tomorrow from CloudBreak is from the first manufacturing run, so it will likey come with 57.5mm backfocus.
Nothing changes with the optics. Just a different metal spacer so the unwashed who don't know how to find proper backfocus can stay with their 55mm (its not even 55mm once you add a filter glass anyway. I suspect that the precision needed for a f/3.8 is nothing to sneeze at). Draw a curve with EAF ∆ vs backfocus ∆ (like using filter glass thicknesses), and the curve should cross zero at 57.5mm or so :-) :-).
But if there is coma at APS-C, the Pleiades goes into the trash. If it works at APS-C, I would be tempted to try my ASI6200MC to see how wide it can go. I think the WO glass will be lucky to work at APS-C; all that I am expecting from such a cheap scope.
BTW, Pleiades name is because of the 7 glass elements. (I would have called it Artemis :-) :-). They should have just call it Subaru :-). For those who don't know what I am refering to, take a look a Subaru car's logo to see what the name refers to. The unaided eyes today can at best see six stars, not seven. The Greeks have good eyes, or something about the missing sister. :-). I wonder if WO knows that one of the glass elements is missing :-):-). I don't think they teach Greek classics in Taiwan.
I really like the fact that there is no external drawtube. That thing should take all kinds of instrumentation weight.
Chen
w7ay I am sure you will test the scope to its limits and if under the 30 day return warranty… just return it if it is trash!
Starizona make an Apex -L reducer for my Esprit 100ED that turns it from a f5.5 to a f3.8 but it only has a 30mm image circle so I think I will stay at 5.5 with my 2600. My 35mm Tamron will be tested at f1.4 so that will be interesting to see how my stars are. Without a filter it was perfect on a fullframe Nikon but with my small pixel 183mc pro cooled camera I am hoping it should be fine with me just adding 0.62mm for the 1.85mm thick uvir cut filter…. Hopefully! Haha
Kevin_A o did you evaluate and conclude your testing on the uvir cut filters in regards to bloat and actually being effective?
OK, go here:
https://bbs.zwoastro.com/d/18401-uv-cut-performance-of-asi26006200mc-ir-cut-window
Note that the ASI2600MC window passes 1000 times more UV at 365nm than a Chroma Luminance filter. And a whopping 7000 times more UV than an Optolong L-eNhance filter. What a bloody joke of a window.
It looks like if I need just a plain IR-UV cut glass (no light pollution bands, etc), I will go to the Chroma-L as my go-to filter in the future. I had been using the IDAS HEUIB before this (for years, now). You can buy four HEUIB for the cost of the Chroma, and you can buy twenty four SVBONY UV-IR cut filters for the same amount of money :-).
Niote that if the SVBONY is the same OEM product as the Optolong IR-UV cut filter, it is pretty poor. See the link for the Optolong. 10x less UV than the ZWO camera window though :-). A 10000 ADU blue halo becomes a 1000 ADU halo -- better, but no cigar.
Chen
Kevin_A did you happen to test the Optolong L-Pro or the Svbony uvir cut filters as they are very popular?
Nope. I have zero interest in anything from SVBONY. Waste of time imaging with them.
But I did buy one from Amazon to measure, so it must be somewhere in the house. I think I had used the filter holder to hold some Baader glass because the Baader did not thread into a ZWO filter drawer. I'll see if I can find it. I usually throw cheap glass like Tiffens and SVBONYs away; keeping the holders for other uses. I'll look for it, but need to wait for night time to get the room dark enough -- perhaps not, if it leaks UV as strong as the Optolong IR-UV cut leaks UV.
After seeing the numbers on the Optolong UV-IR Cut filter, I will probably thrash its glass too, and use the holder to hold Baader glass instead. I had used it as a prefilter for the NBZ-II with that disastrous huge halo, but it looks like I need to make another pass on a prefilter, using the Chroma L glass. There is probably next to zero 21st century anti-reflection coating on that thing. If I no longer see a halo, and the SVBONY measures out to have similar UV suppression to it, I would highly recommend that you thrash the SVBONY.
With optics, good things are seldom cheap.
If I remember correctly, the SVBONY's glass did measure out with a thickness gauge to have identical glass thickness as the Optolong UV-IR cut. Notice the huge difference between the Optolong UV-IR cut's UV performance and their L-series filters -- they are not from the same universe. There is a big cost difference between the Optolong ($65) and the SVBONY ($25). There is always some fishy stuff in the astronomy world -- like the markup on the Radian Sharpstar re-badging (before OPT went belly up).
Hey... look what UPS just delivered.
Will see if I can drill some holes in an EAF to mount it (or use my 'big hole plate") so it does not stick below the plane of the Losmandy dovetail plate. The pictures I have see with the ZWO EAF mounting plates is that it will stick below the Pleiades' dovetail.
Chen
P.S., guess what, CloudBreak dropped the new WO spacers in two plastic bags, into the Pleiades 68 box. Presumably that would make it a 55mm back focus (with no filter glass). WO is pretty fast about upgrading customers.
The backfocus adjuster is 18mm +/- 2mm, the ZWO filter drawer is 20mm, the camera flange is about 17.5mm, placing the focal plane nominally at 55.5mm +/- 2mm without glass. With 2mm glass, the EAF ∆ zero crossing should be close to the center of the backfocus adjuster.
With the new adapter, I should be able to adjust for proper backfocus without adding any extra spacers/stop rings than the backfocus adjuste... we shall see . The optical path of the new 54mm adapter is 5.09mm (constant all around -- so may be OK with tilt without having to go to PreciseParts). The OTA end has a 60mm/1.0mm thread -- odd diameter. Here is WO adapter, Askar backfocus adjuster and ZWO 54mm filter drawer...
I haven't looked at the thickness of the original 54mm yet... haven't gotten that far. Probably between 2mm and 3mm.
Chen
Kevin_A I probably won’t hear from you for a few days now!
I found the SVBONY UV/IR cut filter, will measure it tonight.
Received email from FrontPanelExpress that they have shipped (are shipping) the Rikonon plates, so I should get that tomorrow.
Original Plieades 68 adapter is 2.89mm thick. Difference of 2.20mm from the new 54mm adapter.
Tube rings are 89mm in diameter, felt on half the circumference of a ZWO 90mm fits perfectly (borrowed from my Sigma 40 setup for now), so I will be jetisoning the heavy WO tube rings and replace with two ZWO camera tripod mounts. Off to buy them now.
Chen
In the meantime, I "borrowed" another 90mm ring from another mount:
Actually, the tube is tight enough in the 90mm ring without extra felt. Note that I jettisoned the ZWO tube locking handles, drilled out one side of the ring a little , and replaced stainless steel button head bolts. Æsthetics, eh?
Eventually, a rack handle will go between the ZWO camera rings.
Chen
Kevin_A so who makes that backfocus adjuster?
Would you believe Askar?
Two sizes for telescope end M48, and M54. Camera end is M54 for both variants.
Nice and smooth compared to the Baader microfocuser, and it does not rotate the image. I would use it as a microfocuser if I stopped using electronic focusers; it is that smooth. Min depth is 16mm, max is 20mm, so they call it 18mm +/- 2mm. So 4mm per 360 degrees- a little low resolution as a microfocuser, but way more resolution than needed for backfocus. The Baader is something like 0.75mm per 360 degrees, or 0.5mm, I forgot their thread pitch now.
Change filter glass, adjust the backfocus adjuster based on the label onn the adjuster, and you are done. No fiddling with shims, removing camera, etc.
As I mentioned earlier, adjusting the focus is the wrong way to compensate for filter changes if you have a reducer or flattener. You need to adjust the backfocus. But this hobby has a lot of uneducated rule of thumbs. Like they never took Physics and Calculus in high school. They think an EFW is all they need when they change filters, without having to step outdoors to readjust the backfocus. Result: bloated corner stars.
Temperature changes require focus change. But changing filter glass needs a backfocus change.
I have some M72 adapters to try to place a filter drawer/wheel before the FSQ flattener. If that works, I can use focus to compensate for filter glass changes. No need to go outdoors, when using a filter wheel.
Chen
Kevin_A much better with the Losmandy plate!
I had over time converted completely to Losmandy plates (and ARCA Swiss for guidescopes). The Vixen plate is a joke.
OK, EAF attached to the Pleiades without the EAF sticking down.:
The ZWO 90mm rings still need 1/2" (+delta ) worth of riser, but it looks more streamlined than the clunking William Optics stuff. But... would you believe that the tall riser is needed really to clear... wait for it... the stupid focus knob that I will never use! I will look to removing the slow motion side of the focusing knobs next.
The EAF is in, so I can play with EAF ∆ to measure backfocus when the skies clear (perhaps in a weeks' time).
Chen
OK, have one more thing to do -- I have to get another Thousand Oaks aluminium cell (removing the filter film) that fits the dew shield of the Pleiades 68, so I can attach the 82mm Kase Bahtinov mask. No way in Haides am I going to use the rough cut-out plastic toy Bahtinov mask that WO puts on their tube caps. Can you imagine focusing a f/3.8 scope with that junk?!
With the correct amount of cork and felt, the Thousand Oak tube cells are ideal to install a Bahtinov mask. I will need a good Bahtinov mask to measure focus change at the corners (EAF ∆).
Chen
Took a look at the All Sky camera, and I quickly cabled everything together (my usual USB-C-hub-on-the-Losmandy-plate makes it easy :-) and added a temporary handle, using something I used on the FSQ a couple of years ago.
BTW, a nice lightweight plate to carry a rack handle is a Arca Swiss dovertail plate! :-) Just need to drill a couple of holes in them. That was going to actually be my fallback.
Cabling is a mess, but it might be good enough to play with:
Main problem is going to be the Bahtinov mask, so I may not be able to get accurate EAF ∆ between center and corner to estimate accurate backfocus. I may just need to do trial and error approximation, but at least the adjustments are easy (no need to touch camera and shims) and it is not cold outdoors :-).
Temperature is mild, so I may not be able to find out how the focus changes with temperature, either.
The setup is defintely back heavy. I will need to make a handle that is mounted further back. The camera rotator is smooth as silk, by the way. Feels very much like the rotator on my Baby Q.
With skies like this, no SVBONY tonight.
Chen
"Early returns" :-) :-)
OK, the WO Bahtinov mask is truly trash. So, I didn't use it. I think, howvere, that I can remove the clear plastic mask from the lens cap. That leaves a 86mm or so hole. I can then glue a 92-82mm stepdown ring (in reverse, remember that trick?) and the 82mm thread can be used to take the 82mm Kase Bahtinov mask. Will try that tomorrow if I can find a stepdown ring in my stash.
OK, so I did the usual subjective backfocus adjustment: i.e., change backfocal distance, mount Bahtinov mask, come back indoors, focus the center star, go outdoors to remove the Bahtinov mask, come back indoors to look for a corner star to see if it is better or worse. Rinse and repeat a few dozen times.
I started with the new M54 spacer (presumably needing nominal 55mm backfocus), the 18mm backfocus adjuster set to 18.3mm, a ZWO 54mm filter drawer (20mm), a Chroma L filter (3mm glass), ASI2600MC.
The mechanical distance is 18.3 + 20 + 17.5 = 55.8mm. WO wanted 55mm + 1mm (chroma filter glass) = 56mm.
No cigar! Coma at the corners of the APS-C frame.
I started adding to the backfocus in steps of 0.2mm untill I reached +1.7mm. No joy.
I then step downwards. At -0.5mm, it started looking better. -0.7mm appeared too much (this is why I really dislike this way to bckfocus adjustment, there is no objective way to tell how much and what direction one is off.
So, I dialed in -0.6mm.
OK, at this point, I am 0.9mm away if the backfocus is really 55mm. I.e., my mechanical backfocus is now 18-0.7+20+17.5 = 54.9mm. But that is with a very thick (3mm) filter!
Interestingly, I would be more correct had I used the original M54 adapter! One wonders if they had two set of people collimating the first run of scopes, and one group actually collimated to 55mm.
Anyhow, with this subjective backfocus adjustment, I see this:
and almost more importantly, this:
Not that shabby, really, especially considering this is f/3.8, and this is a single frame, not a stack. I see a halo from the very bright central star, but that is not the concern of today's experiment :-).
The corner stars are pretty round. I should be able to dial in (objectively) better once I have a usable Bahtinov mask to get reliable EAF ∆ measurements. And stacking will give even more symmetrical star shapes.
The full image is here:
http://www.w7ay.net/site/Images/-0.6mm.JPG
Don't think this OTA will go to the trash. Donno why it was trashed on Cloudy Nights. Looks fine to me, if you know how to adjust backfocus.
One day, I will go adjust the tilt at the bottom left/right -- shows up on Siril's tilt trapezoid above, and also on the bottom right panel of the aberration reporter. Usually that amount of tilt is no big deal, but at f/3.8, I may have to waste a night adjusting it. But the Siril tool should make it not too much work. The tilt adjuster in the Pleiades is actually a 4-point adjustment. This should make it relatively easy to remove my tilt once I align the camera's angle to the OTA's angle.
Notice that the average of the star size at top two trwpezoid nodes is 3.29, and the avge of the bottom 2 is also 3.29. So, it is just a left-right tilt of the bottom edge.
So far, it easily wipes the floor with something from Askar, both in speed, and in APS-C coverage. I am retiring the FRA300 -- perhaps retrieve some parts, like the EAF from that set up.
Chen
w7ay that 1 corner should be able to be adjusted out very easily. I do notice a tiny bit of lateral CA but nowhere near what I have on my slower big triplet and on my FRA300. My Rokinon only has a bit of longitudinal CA and that is easily removed. Strange how WO decided to use a focus knob the size of a Mack truck! Great results so far.
