My bi-polar dream

[kalasinman]

Admittedly it will be a year or so before I can go CCD. Modding my Nikon currently. So with a pensioners budget, I find myself comparing the QHY9 with the large Kodak chip and the QHY21 with the very sensitive and low noise, but smaller chip. QHY9 and 3 NB Baader filters about 2.5K USD plus shipping. With same filter set and a wheel, the QHY21 comes in about $500 more.

Apparently the QHY9 has a mechanical shutter that mandates 2 second exposures for flats, which sounds ...inconvenient.

I've set both up in Stellarium and my scope, and the FOV of the big chip looks attractive. Do they still have the same shutter on the QHY9?

[Physopto]

Smaller chip and you loose photons!

Derek

[kalasinman]

If the photons aren't in the frame, that isn't an issue.The considerably higher QE means per unit of time, more photons in the frame. Higher QE at Ha means better emission neb sensitivity. Lower noise is always a good thing, too. These are the upsides of the Sony chip, as far as I can tell.

Kodak chip is bigger, so wider FOV, not a small consideration. It also has a deeper well depth, potentially making better star color. IT'S CHEAPER!

My downsides of the Kodak : mechanical shutter, other than 2 sec minimum flats (what other bad things come with this I don't know), lower QE overall and even lower at Ha, higher noise.

Downsides for the Sony : more expensive, smaller chip means making mosaics more often (not sure if that would be a big issue or not for me), shallower well depth.

For me, this would be a huge expenditure, so potentially a once in a lifetime (turn 70 next year :-) ).

Just to be clear, OSC is not on the table. I already have a DSLR.

The reason QHY is preferred is simply that a 10 degree centigrade increase in cooling is huge for me in the tropics.

[gazza]

Hi,

I've just been through a similar decision process and ended up with a QHY9S + CFW2 7 position filter wheel and a full set of Baader filters. I looked VERY seriously at the Sony chipped cameras, but found that the smaller chip yielded a too small field of view. The Higher qe of the Sony chip is also a bit of a non issue as at a given focal length, the slightly larger pixels of the 8300 chip gather more photons (assuming that the arc sec per pixel size is going to give you decent resolution). I also looked at pics taken with the Sony, many were mosaics, and the need to do twice the work to get a decent field of view, also more than outweighed any nominal efficiency difference. Any caveats here relate to what scope you are going to use. I will be using both a TSA120 at f5.6 and a CPC1100 at f7.5 (using a Starizona reducer corrector which after testing, I can confidently say turns a standard SCT into a dream long FL imaging machine!). The QHY is on my bench (haven't imaged with it as the filters only arrived yesterday) and in a room centrally heated to 23C it was using 11% power to stay at -15C. Since in Australia it is not uncommon to have 20C nights, the cooling was very important....

YMMV

cheers

Gary

[kalasinman]

Thanks Gary, as far as cooling, a QHY in either case is part of the decision as I image at 25c+ here. One concern about the QE is that the Sony chip has a net higher QE at Ha. This would mean, I believe, less star bloat and a clearer target.

I'd be using my 150/750 f5 newt

The biggest issue is, as you pointed out, the chip size and resulting FOV.

FOV in degrees with:

D5100 = 1.2 x 1.8

Atik414ex = .5 x .65

QHY21 = .7 x .82

QHY9  = 1.03 x 1.37

Using Stellarium to compare framings with common targets, even the QHY9 won't get the Rosette, Heart, or Pleiades. On the other hand, I like the framing of M1, M13, M27 for example much better with the QHY21. Severely cropping to a frame with large pixels will result in less resolution.

 I'll have the modded D5100 in place soon and see how I like it.

Because of my high imaging temps I had been thinking of replacing the DSLR with a cooled CD, but now I wonder if a strategy including the DSLR to give a choice of FOV might be better. In any case, I'm adding in AT and can see that I'll have to learn mosaic making eventually.

It's a good thing in a way that it will be a year or so before I can purchase any CCD.

[Physopto]

You could try the QSI 683Wsg8 partly because of the larger chip but also it can be water cooled. So in +25degrees heat you can cool with a bucket filled with ice and water. You will get probably down to -10 at least and possibly further. I would get in touch with QSI to find out if there would be any condensation problems with the outside of the CCD window, not the inside. I'm pretty sure it would work down to -20.

You just need the water cooling block and a very small fish circ pump and some silicon tubing. I'm sure the ice would not be a problem over there.

Shutter on the QSI is operational down to I think 0.03 seconds.

Derek

[kalasinman]

At over 3K USD, out of my budget, and performance no better than the QHY9 mono with wheel for 2K USD. Water cooling? All I can say is nope.

Reviews I've seen say the new Sony chips have quite low noise without extreme cooling. I'd probably go for a QHY version with -40c cooling regardless of which chip.

Charts I've seen put the QE of this chip (8300) at 40% at 700nm and 400nm , while the Sony chip is 70% at 400nm and 60% at Ha.  I do hope to go NB at some point and having Ha sub lengths cut in half with much lower noise is pretty irresistible.

Maybe I'll save another year and go for the QHY22. Bigger FOV with high resolution.

As I've learned with other kinds of tech, better stuff is always in the pipeline, and it seems the next year or 2 could bring big changes. I've still got a lot to learn with my DSLR, and having the Baader mod accomplished (hopefully soon) will open up many new opportunities.

[Physopto]

OK I understand.

The response is 40% at 400nm rising to 60% at 530nm and the dropping to 45% again at 680nm approximately. There is always the second hand market. The 583 is identical in all respects for response but is slower to download(23 sec) and cooling not quite as good (5 deg less). But you can still water cool on it.

You could ask Olly his views on different CCDs.

I hope whatever you pick does the job for you. It is always a tough decision spending the hard earned stuff.

Best regards,

Derek

[kalasinman]

I've read Olly's views, but I can't afford an Atik 1100 ;-) . I kept using Stellarium with the different CCDs plus my DSLR plugged in. I was surprised when I realized that the smaller chip gave me a FOV I missed with the DSLR. New targets and all.

Not many folks image at 25c as I most always do. Wanting to double down with better cooling and a cleaner chip is really large on my list.

I've got lot's of time to decide. Sorry if I seem to be wasting others time here. It really helps to have the conversation. Not only to hear other opinions but to help explore my own feelings about it.

Having just started a year ago last month, I'm like a kid in a candy shop.

I love wide field too, little OT, but I'd like to explore CCD on camera lens as well.

[Physopto]

You are definitely NOT wasting anyone's time. I think everyone goes through the should I shouldn't I thing. Money is money and not to be wasted, at least not mine .

I think I spent about 18 months in that stage, but learned mostly what I wanted. We still mess up at times unfortunately. The QSI CCDs go down 40/45 degrees below ambient at 85% power. I have never tried that though. I intend to try out the water cooling using an antifreeze here in the UK. a) to reduce power in the camera, and to see how cold I can image at, for thermal noise. I don't have a problem but since I have the water cooling block why not!

I only know what I know so if I can't help there will be others very willing. So ask away.

Regards,

Derek

[gazza]

The QSI CCDs go down 40/45 degrees below ambient at 85% power. I have never tried that though. I intend to try out the water cooling using an antifreeze here in the UK. a) to reduce power in the camera, and to see how cold I can image at, for thermal noise. I don't have a problem but since I have the water cooling block why not!

I only know what I know so if I can't help there will be others very willing. So ask away.

Regards,

Derek

Just be careful that you don't take it too cold --- Kaf8300's are only rated as OK to -5 deg C by the chip makers. Most ccd camera manufacturers suggest -20c is as low as you should go. Any further risks damage. Good cooling is mostly important in warm areas, so you can get to -20, not to try to hit -35. I know of a kaf 8300 that cracked at -35 c and had to be replaced!

Gary

[Physopto]

The QSI CCDs go down 40/45 degrees below ambient at 85% power. I have never tried that though. I intend to try out the water cooling using an antifreeze here in the UK. a) to reduce power in the camera, and to see how cold I can image at, for thermal noise. I don't have a problem but since I have the water cooling block why not!

I only know what I know so if I can't help there will be others very willing. So ask away.

Regards,

Derek

Just be careful that you don't take it too cold --- Kaf8300's are only rated as OK to -5 deg C by the chip makers. Most ccd camera manufacturers suggest -20c is as low as you should go. Any further risks damage. Good cooling is mostly important in warm areas, so you can get to -20, not to try to hit -35. I know of a kaf 8300 that cracked at -35 c and had to be replaced!

Gary

Hi Gary,

Many thanks for that I'll look into it properly. I had no idea as QSI said it could easily reach -20 degrees. As I keep saying we learn some thing new each day.

It may have been not warmed up properly, but definitely worth knowing. Some times when things go wrong and the usb shut down (low voltage or a fault) goes it just alarms and shuts down the cooling without MaximDL the chip warming up properly.

Thanks again.

Derek

[swag72]

Here's my thoughts on it having ummed and ahhed over the exact same issue last year. 

I went for QSI as I wanted the integrated all in one filter wheel and OAG and I needed good cooling as the Atik I had over here was woeful at best...... so I was torn between the 690 (Sony chip) or the 683 (Kodak chip)

In the end I went for the Sony chip, but really do wish now that I hadn't and gone for the real estate of the 8300 chip instead. Mosaics are all very well and good and I do quite enjoy doing them, but they can be soul destroying. 

The good thing about the QSI and the Moravian Kodak chips is that their filter wheel carousel is close enough to the sensor so that you can still use 1.25" filters. However, if I was buying from scratch today I would definitely get a Kodak 8300 and the unmounted filters as they give you a little more breathing space and aren't much more expensive than the 1.25". 

[Physopto]

Well I've just been on the QSI website. Turns out that they are saying their cameras are capable of going down to -40 C at which point the camera actively stops cooling any further. But their links to Kodak 8300 documentation states clearly that the absolute minimum cooling for the 8300 chip is -10 degrees Celcius. So why not a clear warning on their website and in the documentation?????

Derek

[kalasinman]

Interesting Derek. For me, -40c of ambient usually would put me -15c,. Latest improvement in heat sink apparently puts QHY down to -45c of ambient.

I still have to admit that with my ambient temps, readout noise of 8-10 e- compared to 5 e- with the Sony seems quite high. Why is this not significant?

[perfrej]

I think he meant that they stop cooling at -40°C, not 40° below ambient.

Readout noise is much more about the electronics than the absolute number of the chip. Here, the more expensive cameras excel as they have better read electronics. Personally, I have found the QSI KAF-8300 implementation quite good; much better than the SBIG one I also have.

The next Sony sensor should be interesting! Count on a few years before anyone gets it working properly in astro, and pray it will be available in monochrome!

/per

[Earl]

my qsi is also better than the atik 383's i had

[gazza]

Interesting Derek. For me, -40c of ambient usually would put me -15c,. Latest improvement in heat sink apparently puts QHY down to -45c of ambient.

I still have to admit that with my ambient temps, readout noise of 8-10 e- compared to 5 e- with the Sony seems quite high. Why is this not significant?

You need to look at the ratio between well depth and read noise:

ICX674 read noise -5e, well depth 15000

Kaf8300 read noise -8e, well depth 25500

There is no practical difference in the chips in this area. The tiny pixels /high QE are more than offset by the larger pixels at any realistic focal length. You are concentrating on specific specs, without looking at them as a whole :-)

​Be careful when concentrating on just a few specs.......

cheers

Gary

[perfrej]

True, Gary, very true!

/per

[kalasinman]

I really appreciate the input. I guess one thing that I haven't been clear enough about is that my total projected budget for CCD, wheel and filters will probably be 3K USD at the high end.

[Physopto]

Interesting Derek. For me, -40c of ambient usually would put me -15c,. Latest improvement in heat sink apparently puts QHY down to -45c of ambient.

I still have to admit that with my ambient temps, readout noise of 8-10 e- compared to 5 e- with the Sony seems quite high. Why is this not significant?

Hi,

Could not answer last night or I would have got my head in my hands!

Per is absolutely correct -40 deg C not below ambient. Probably to save camera electronics.

The 683 can go down to 45 deg below ambient at 80% power. The 583 40deg below ambient at 80% power.

Gary is also absolutely correct think in %. Of full well capacity.

5/14000= 0.000357 QSI 690

9/25500= 0.000352 QSI 683

Approximate figures. Nothing in it !

This web site on QSI makes very interesting reading.

http://qsimaging.com/ccd_noise.html

I think a lot of the time "you pays for what you get" is the way to look at it.

Not all cameras are equal even with the same chip used!

I listened to others here on SGL and other sites, also spent a year or more reading up before taking the plunge.

Rushing in mostly wastes money unless very lucky I think.

QSI are expensive for a reason.

As to chip size

690 has 12.48 x 9.98 = 124.55 mm2

683 has 17.96 x 13.52 = 236.85 mm2

683 has 1.9 times the area although less pixels but better well capacity. Means longer subs possible!

If you consider a FSQ Tak with 40 mm diameter imaging circle that's 1256.64 mm2 area. With the 683 you loose approx 71% of the photons incoming, (but you can never image a circle anyway), with the 690 you loose 90% of the incoming photons !

In truth the loss for the 683 compared to a same aspect full sized chip that would fit into the imaging circle (if such a chip exists) would be only a loss of approximately 59%.

For the 690 chip it would be about 85% loss, as it is roughly half the size of the 683 chipped camera.

As I think Olly has said real estate pays!

Derek

[kalasinman]

Derek, please read my most recent post and put it in perspective. I am very aware of much of the good advice already given. Much of it by people who can afford TAks, 10 Microns, and Atik 1100s. Although I truly rejoice in their good fortune, I must be realistic.

I have never seen an ad for a CCD that claimed cooling to -45c. Every one I've seen claims degrees below ambient.

[Physopto]

Hi,

You are mistaken.

I did not say -45 degrees C . I did say -40 degrees below ambient. Also QSI claim that their Cameras stop cooling at -40 degrees C. So if I guess you cooled in the Arctic for some weird reason the camera would not keep trying to cool below that figure. Or if you used the water cooling with an ice bath for the cooling water medium it would also stop at that figure. As I said possibly a safety device for the camera. Condensation would also be a definite problem then. Or chip fracture as has been mentioned above in the posts.

I don't have unlimited funds as I suspect as do most others. I just saved up over a long time.

Apogee make a camera that cools to 65 degrees below ambient !

I am trying to help you with the facts as I see them not make life more difficult. Once you know you can always choose whatever suits you and your pocket. To be honest if I saved up for another ten years I could probably afford some thing much better.

Mind you the wife would have strangle me long before then .

Derek

[kalasinman]

Putting things in perspective, as I said in the beginning I'm a pensioner. I live in an economy where the cost of a QSI CCD represents 1/3 of the cost to construct a 2 bedroom house. I'm renting right now. It also represents more than the total cost of my present kit including: scope, mount, DSLR, guide cam, OAG, software, laptop and cables and adapters. Maybe I should just not consider a CCD at all, as I can't justify a thousand dollars extra to gain a percentage point or 2. At this point having a CCD at all would be a huge step.

[Physopto]

Putting things in perspective, as I said in the beginning I'm a pensioner. I live in an economy where the cost of a QSI CCD represents 1/3 of the cost to construct a 2 bedroom house. I'm renting right now. It also represents more than the total cost of my present kit including: scope, mount, DSLR, guide cam, OAG, software, laptop and cables and adapters. Maybe I should just not consider a CCD at all, as I can't justify a thousand dollars extra to gain a percentage point or 2. At this point having a CCD at all would be a huge step.

I get the point, that is a frightening cost comparison.

Still whatever you do good luck.

Derek