First Light with new ASI585MC Pro.

Kevin_A

Tested out the new cooled 585 camera last night at Unity Gain 198 on my 115mm triplet. My target was M51 the Whirlpool Galaxy and M81.
Just 3 hours of 180s subs on M51 and only 30 minutes on M81.
Un cropped and quick process in Siril/ Lightroom only.
Low resolution upload due to file size requirements. I still need 7 more hours to tame the noise and increase DR.
I am happy with the overall results and will try again at Gain 150 to reduce oversaturation of bright stars due to lower FWC at Unity.

w7ay

Kevin_A new cooled 585 camera

Very nice, Kevin.

I have one of them on order -- good to see small pixel cooled camers for use with galaxies, and where sensor size is not an issue.

By the way, after years (literally) of chasing wide FOV lenses, I have converged on, ta da, the relatively cheap Samyang 135/2 (the Rokinon T2.2 version)! From initial tests, that is one sharp lens, but I need star fields (when clouds allow) to know for sure.

I had started the quest a while back with a Canon 100/f2.8L, then went through Askar ACLs and FMAs, and the Samyang 50/1.2 and the Sigma 135 ART... all gave mediocre stars.

I went for the Rokinon version of the 135 becase it is actually lots cheaper at Amazon than the Samyang 135 with RF mount, and it has the "follow focus" gears built in (the f-stop ring also does not have click stops, per typical cone lenses). EAF directly mounted (same Astrodymium rings for Samyang 135 work fine, and the EAF is mounted directly on one of the rings by drilling both an EAF and the Astrodymium).

Hoping to catch the Corona Borealis region as a "before" reference image before the Nova burst for an "after" image." The 135 with APS-C sensor is actually a reasonable framing too for the constellation. (6200 in the above picture, with the integral EOS mount+filter drawer -- new style drawer with no -- well almost no -- light leak.)

By the way, if you are using step-down rings to control your Samyang f-stop, try adding a UV camera-lens filter, but with the filter glass removed. The filter's aperture opening is lots cleaner than a typical threaded step down ring opening. The diameter needs to be re-measured, of course, since a 49mm filter has a clear aperture that is much smaller than a 49mm step down ring.

Chen

Kevin_A

w7ay I have been using the 135 f2 for a long time. I tested mine out when I first bought it as they are notorious for lens element decentering. I focused in the centre on a far away forest and then moved the lens to look in each corner and edge at the trees to make sure each half and each corner was similarly sharp. My first lens had one side that was softer so it was decentered and I sent it back to Amazon and ordered another immediately. That one was a keeper and tack sharp. The price vs sharpness is fabulous to say the least. I shoot mine at only f2.8 as at f2 it had diffraction iron crosses and at f4 the stars get too many spikes for my liking.
I like widefield with mine. Very clear but it needs star removal all the time! Star Magnifier! Haha

Kevin_A

w7ay if you find that you have a bit of slop or sag or gap in the filter drawer fitting to the Rokinon lens as I did you can fix it easily by adding Tuck tape as shown. It works great to elliminate tilt due to sloppy lens to adapter fit. I then use a blue rubber band (from broccoli bunches) over the connection to eliminate any light leak possibility… fyi.

w7ay

Kevin_A I shoot mine at only f2.8 as at f2 it had diffraction iron crosses and at f4 the stars get too many spikes for my liking.

That is why I use stepdown rings, and on top of it, use the camera filters with the glass removed, to provide an even cleaner circular aperture. Fourier Tranforms of non-perfectly circluar aperture gives spikes of all sorts.

For 77mm (Samyang and Rokinon front filter thread), I currently have

77mm->52mm step down with glassless 52mm filter that gives 47mm clear aperture, or f/2.9 for 135mm focal length.

77->49 + 49mm glassless filter -> 43.5mm clear aperture -> f/3.1 at 135mm f.l.

77->40.5 + 40.5 glassless filter -> 35mm clear aperture -> f/3.85 at 135mm f.l.

Chen

w7ay

Kevin_A

Kevin, I found a good combo to get f/4 from the Samyang/Rokinon.

The cheap Tiffen 39mm filter with the glass removed has a clear aperture of 33.7mm, which givesreally close to f/4 for 135mm.

https://www.amazon.com/gp/product/B0BBQ4GM9C

So, step down the 77mm filter thread to 39mm thread, and insert the glassless "filter." The aperture appears quite clean and round.

Since getting my Rokinon, I have increased my existing collection of step-down/clear-filter combos to these:

The 37mm and 39mm needed two steps of step-down, since I could not find any 77mm-39mm and 77mm-37mm step-down rings. So I chose 55mm as the intermediate; 77mm-55mm is one of the existing step-down rings.

Darn lens should be clear as a bell at f/4. (Sorry for mixed metaphores. :-)

I am always nervous about placing an iris at some place other than a nodal point of the lens. But so far have not found that it increased the vignetting. And using a glassless filter gives a very clean aperture with no diffraction spikes. I have not seen anyone else mentioned using apertures from camera filters, by the way, but just using step-down rings themselves, which do not have a clean circular aperture due to the filter thread. $10 to get rid of nuisance diffraction seems worth it.

Chen

w7ay

Kevin_A if you find that you have a bit of slop or sag or gap in the filter drawer fitting to the Rokinon lens as I did you can fix it easily by adding Tuck tape as shown.

The ZWO filter drawers, after at least 3 different redesigns, are finally pretty usable.

The latest drawers have the filter holder seated flush with the body of the drawer, and finally (mostly) solved the light leak problem of the previous ones. I threw about a dozen old ones away (actually sent to my dealer so he can give them away for free to people who are willing to apply electrical tape each time they change filters). The new EOS flange is likewise pretty good and very tight. I remember an older version (with the round push pin) that had a wobbly interface, and impossible to use (that is why one of my EOS filter drawer is from Starizona).

Between the ZWO EOS filter drawer and custom drilling and tapping the EAF and camera rings, the Rokinon Cine setup is actually quite minimalistic. Everything (including a USB-C hub) on a single 7" ADM Losmandy dovetail plate. Added my standard rack handle of course.

BTW, since the small body of the 585 precludes it from using the M54 tilt plates, I cobbled up enough Frankenstein spacers to replace that black T2 ring with a 54mm interface that maintains 11mm optical path, so the ASI585 can simply be a drop in replacement for my 6200 with the 54mm tilt plate. This, while waiting for PreciseParts to mill a proper 11mm M54-M42 female-female ring for me. PreciseParts have improved their turn around time a lot -- now perhaps down to less than a week before they ship. So, just waiting for camera and weather now. Most dealers are out of the cooled 585, and I got CloudBreak's last one. I had initially thought that it is just a poor man's cooled camera; but the smaller pixels swayed me -- the 6200, 2600, 533 pixels are just too large for my small scopes. Before the 6200 series, I had used the ASI071, which also had large pixels, albeit not as large.

Chen

w7ay

Kevin_A Tuck tape

I need to squirrel away some of that. I have the 10 mil thick UHMW tape (for alt-az mount surfaces :-), but I see the Tuck tape are just 3 mil thick.

Chen

Kevin_A

w7ay I found that both my older adapter drawer and lens were both a bit loose and 3mil was perfect.

w7ay

Kevin_A

So far so good. Some thin clouds, but I can see enough stars. This is APS-C at f/3.85 (using a 40.5mm glassless "filter" as aperture -- no star spikes, even on Regulus). Notice that ASIAIR's star detect tools give pretty even HFD across the field.

It can probably stand a little bit more spacing to the sensor; I'll play with that soon.

Corners of full frame is not that great, but the extra spacer might help.

FMA 180p + ASI178MM (gain 27 dB) as autoguider.

Chen

Kevin_A

w7ay I found that this lens is very critical for backspacing. So much that I use a vernier to measure the stack of parts. Even having filter changes that are 1.85mm vs 2mm is enough to have to change my shims.

w7ay

Kevin_A Even having filter changes that are 1.85mm vs 2mm is enough to have to change my shims.

The FSQ-85 is sensitive to even 0.1mm of backspace too (if you care about getting small stars) for Takahashi's native 56.2 mm number. (I have not yet figured out why such weird backfocus number, but it is uniform for all of their FSQ flatteners and reducers; and they are serious about the "0.2mm" part :-).

I have a couple of sets of the Agena Blue Fireball metal spacers that go from 0.1mm to 1mm in 0.1mm steps to handle the Taks. None of the silly 3D printed spacers (and Baader's metal spacers don't have enough resolution); thank god for Blue Fireball (Agena house brand?).

https://agenaastro.com/blue-fireball-9-pc-fine-tuning-spacer-ring-set-for-m54-threads-0-1-to-1-0-mm-s-set9.html

Their M54 tube spacers are also quite good -- threads almost as smooth as the custom stuff from PreciseParts.

Heavier clouds came in by the time Corona Borealis appeared over the tree tops, so never got to take my pre-Nova reference photo.

The price vs sharpness is fabulous to say the least.

I concur. This appears to be one sharp lens for its price (especially after having gone through Canon-L and Sigma-ART lenses). I tried both f/3.85 and f/2.9 last night, and the f/2.9 does not appear to suffer much at all from f/3.85 for APS-C frames. (Weird numbers are from step down rings and the camera filters after removing the glass.) Its usefulness is somewhere between APS-C and full frame (I was testing with an ASI6200MC). I might stick to f/2.9; less than 1/2 stop difference though, FWIW.

Chen

Kevin_A

w7ay I ended up settling on f2.8 after all my testing. I would have liked to have gone to f2.4 but it started looking a bit off. Another cheap but fabulously sharp coma free, astigmatism free lens is the Tamron SP 35mm f1.4 lens. I was hugely impressed and found it so much better than the Sigma A 40mm f1.4 lens at way less of a price. I am now in the process of buying a SW Esprit 100ED scope for deep space targets as it seems very nice too.

w7ay

Kevin_A Tamron SP 35mm f1.4 lens

As long as it is not Chinese glass, I am willing to try :-).

My trees would only allow something like 1/2 hour exposures for 35mm type focal lengths, though. I have the Samyang XP 50/1.2 for meteor showers, and for that, I don't even track. Just point to a clear spot in the sky. Might be able to do the same with a 35mm. I am not impressed with stars on the 50/1.2, so I am willing to try something else. 35mm on APS-C is not far from 50mm on full frame.

Chen

w7ay

Kevin_A Tamron SP 35mm f1.4 lens

Wait... can this lens be manually focused without being attached to an DSLR camera?

P.S. Back to the ASI585MC -- UPS says it is coming tomorrow. Yeah, snatched the last one from my favorite Seattle telescope store.

Chen

Kevin_A

w7ay I know the SP 35 says designed in Japan on it. With this lens on my Nikon Z7 I remove it from my camera while it is at f1.4 with the camera still on and it stays at f1.4. I shoot it at f1.4 as well as it is very sharp wide open.
Here is a low rez stacked shot of 30 minutes of 60s subs at f1.4 on a SW tracker and Nikon Z7.

w7ay

Kevin_A I know the SP 35 says designed in Japan on it.

Manual focus?

Chen

Kevin_A

w7ay both manual and auto. I always use manual. No VR so that is good too.

https://www.tamron.com/global/consumer/lenses/f045/spec.html#nav

w7ay

Kevin_A both manual and auto

OK, it is the next lens to look at after getting the Rokinon 135 optimized (using the English meaning of optimize, and not ZWO's usage of that term, which is a bug fix).

Perhaps get it ready for Perseids.

I have given up on the Milky Way from here. It is towards the south, and the sky pollution there is like a Bortle 8. I can get something like "looks" like the Milky Way, but nothing like what I saw as a kid in Asia.

By the way, even the ASI585 is good for a 4.7º x 2.7º field of view with a 135mm lens -- easily frames M42 and Running Man, not to mention M31. With slightly better pixel size than an ASI6200. Problem would be the dynamic range for M42 and M31.

Chen

w7ay

Kevin_A https://www.tamron.com/global/consumer/lenses/f045/spec.html#nav

Darn... just when I have started to standardize on 77mm filter thread (and step downs) as apertures for my lenses. :-).

Chen

Kevin_A

w7ay one thing I did notice with the cooled 585 was the amount of hot pixels at HGC. I used Unity gain 198 and it was reduced greatly but that 198 setting still seems to have a bit too little FWC for my broadband imaging and bright stars really got saturated fast at f5.6 on my 115mm triplet. I am going to test gain 150 as it seems like a good balance and the extra noise will get eliminated with more total integration. Using LGC has a normal amount of hot pixels, but HGC just goes nuts!

w7ay

Kevin_A the amount of hot pixels at HGC

Hope this is not a trend. There are already zillions of hot pixels in the ZWO 2600/6200/533 series. Have you tried gains pf 20dB to 30dB with those cameras? More hot pixels than bright stars :-).

Chen