9 replies to this topic

[f29pc]

I had my Samyang 135 with an OGMA 26C (IMX571c), worked out great. I wanted to go a little longer on the FL so I picked up a new RedCat 51 (iii), moved the 26c to the RedCat and loved it even more. Now the 135 sits on my desk with a full Astrodymium and EAF setup and no camera. Going through my old camera collection, Ive got a QSI 683 and a ZWO 1600mm (w/filer wheel) and a full set of 31mm astrodon's. I'm looking to do mostly mono narrow band, both cameras still work great. I'm looking for recommendations/opinions on witch camera would give the best results. I feel like the QSI is stepping back into the ccd dinosaur days but it was a great camera. I'd like to hear opinions of one over the other. (I know the qsi might be a little tricky to get the right back focus to work, but I think I can work that out with a day in the machine shop) Thanks.

[Tapio]

You didn't mention which version of Samyang you have.

But of those I would choose ZWO 1600. Because it's somewhat newer and because it has 6.5mm 'back focus' - which helps fitting fw.

[Helyis]

I don't see any valid reason to go for a kaf-8300 camera when you have a 1600mm next to it.

In my opinion, it is worse on every metrics...

[ChrisWhite]

IMO the KAF8300 is a superior chip.  No microlens diffraction pattern, no ampglow, easy to calibrate.... I think it just produces better data.  A little more download time and your sampling is not as good as the 1600, but with a 135mm lens you are already very undersampled so not too much loss there.  You will likely have some weak or bad columns so cosmetic calibration is essential. 

 

I've owned two 1600's mono and one OSC, as well as two mono QSI683's.  I no longer have any of them, and much prefer the IMX series chips (533/571/455).  I've had a bunch of other camera models as well along the way, and the only chip I consistently didnt like was the Panasonic-M. 

 

Good news though, you have both.... so no harm in trying both to see what YOU like.  I cant recall of the top of my head how much backspacing the QSI683 takes up though. Can you fit a lens adapter in there in the first place?

[f29pc]

Good news though, you have both.... so no harm in trying both to see what YOU like. I cant recall of the top of my head how much backspacing the QSI683 takes up though. Can you fit a lens adapter in there in the first place?

The QSI back focus is 35.56mm, I've got the QHY Canon lens adapter that takes up 10 mm of back focus, this puts me at 45.56 mm. Taking the filter thickness (3mm) this should get me really close. I believe I can take the adapter apart and find 1.5mm on the lathe somewhere.. The microlensing is one of my concerns with the 1600. I didn't do much with the 1600 before I put it on the bench and upgraded to a QHY268m.. I ran the QSI683 for a few years and had few complaints.
If I were at my place in Az. I could do a comparison between the 2 in a couple days... Here in the Northeast, getting 2 clear nights in a month is very rare lately!

[dhaval]

QSI all the way. A CCD is still way better to calibrate than a CMOS, and that is definitely true for 8300 over the 1600. 

 

Thanks and CS!

[Tapio]

QSI all the way. A CCD is still way better to calibrate than a CMOS, and that is definitely true for 8300 over the 1600.

Thanks and CS!

What do you mean by 'better to calibrate' ?

All cameras, cmos or ccd, calibrate nicely if done with suitable calibration frames.

People have done excellent images with 1600 camera and my recommendation was based more on back focus distance - which may be problematic using camera optics with filter wheel.

Edited by Tapio, 19 June 2024 - 10:56 PM.

[dan_hm]

QSI all the way. A CCD is still way better to calibrate than a CMOS, and that is definitely true for 8300 over the 1600.

Thanks and CS!

Welcome to 2016!

[dhaval]

What do you mean by 'better to calibrate' ?

All cameras, cmos or ccd, calibrate nicely if done with suitable calibration frames.

People have done excellent images with 1600 camera and my recommendation was based more on back focus distance - which may be problematic using camera optics with filter wheel.

CMOS calibration, especially with the 1600 relies on consistent darks, flat darks, flats and ensuring a lot of things are in coordination. Not that it cannot be done, but it is painful. I also felt that the linearity of 1600 chip was questionable when they first came out. Have folks taken wonderful images with the 1600? You bet. You just need to look at my Astrobin and  you will find a couple of really good images using the 1600. But, if the choice was between the 1600 and the 8300 chip, I would always pick the 8300 chip, especially if it was a good brand (FLI, QSI, etc.). You get a better camera overall. You do lose QE and for narrowband, it is significant loss, but if you have the patience, you can't beat the 8300 for consistency. The backfocus is a separate beast all together. Obviously that has to be factored in, but if that is a non-issue, there is no harm in using the 8300 chip. My recommendation would have been different if the question was 8300 v/s one of the modern CMOS chips. In that case, the 8300 chip loses out everyday - in fact, the 533 is a much better camera in that sense (if one is on a budget). You do lose FOV, but the QE is exceptionally high and the linearity is very good. 

[ChrisWhite]

The miceolens diffraction issue is the biggest deal breaker for me. A 135mm lens will have a very large FOV. Tough to avoid bright stars and the brighter they are the more pronounced the artifact is. There are no easy fixes for it either. Tolerance of it is purely subjective though.