Qhy8/9 - Page 2

AlexN · #21 29-12-2009, 12:49 AM

fair enough

marki · #22 29-12-2009, 01:01 AM

Sorry Alex I am not meaning to be narky but at -20 degrees C I am not seeing a whole lot of noise on the KAF 8300 and this always seems to be the argument of the sony vs kodak debate. You will see when yours turns up, they really are a very nice little chip. I can see where you are coming from with the bigger pixels and I am still to mount my camera on the meade but things are looking pretty good by my eye.

Mark

AlexN · #23 29-12-2009, 01:23 AM

Yeah I hear ya... I've been looking at dark frames from the 8300 based sensors for months prior to actually ordering one, they arent bad at all when cooled below -10c from what I've seen... -20 would be very clean I'd imagine.

My main reason for advocating the QHY8 over the QHY9 (assuming both are OSC) is that the QHY8's QE is better.

marki · #24 29-12-2009, 01:56 AM

Quote:

Originally Posted by AlexN

My main reason for advocating the QHY8 over the QHY9 (assuming both are OSC) is that the QHY8's QE is better.

Don't go there or you will really stir the pot as to the validity of either manufacturers QE claim

. Only one way to settle this proper .... the OP will need to get both cameras and try them side by side through each scope. Pick the winner and sell the loser

Mark

AlexN · #25 29-12-2009, 02:06 AM

Not everyone is so willing to spend money on a trial and error basis as I am Mark...

pmrid (Peter) · #26 29-12-2009, 02:10 AM

Quote:

Originally Posted by AlexN

When comparing the QHY8 vs the QHY9 OSC, the QHY8 is the better of the two providing you dont "require" the smaller pixels of the QHY9...

As Pauline Hansen once famounsly said "Please explain!". Knowing that I will display my ignorance, I'm trying to get my head around the 'pixel-size' as a determinant of suitability. What is the correlation between pixel size and FL or Objective diameter? What makes one pixel size more suitable to a particular scope than another?
Peter

marki · #27 29-12-2009, 02:29 AM

Quote:

Originally Posted by pmrid

As Pauline Hansen once famounsly said "Please explain!". Knowing that I will display my ignorance, I'm trying to get my head around the 'pixel-size' as a determinant of suitability. What is the correlation between pixel size and FL or Objective diameter? What makes one pixel size more suitable to a particular scope than another?
Peter

To put it simply,

long focal lengths --> Big pixels

Short focal lengths --> small pixels

Small pixels on a long focal length scope are wasted as you over sample and the images can appear soft. Big pixels on a short focal length scope leads to under sampling and square stars.

Mark

AlexN · #28 29-12-2009, 02:43 AM

Its all about sampling and resolution Peter.. The 7.8 micron pixels in the QHY8 are suited to longer focal lengths (700mm up to around 2500mm) The 5.4 micron pixels are suited to shorter lengths, 450 ~ 1500mm, perhaps a little longer.

Theres a program available called CCDCalc, where you put in the specs of your sensor and your telescope, and it calculates the field of view in arc minutes and also, the arc-seconds per pixel resolution.

After much reading on the matter, I have deduced that an arcsec : pixel resolution should be about 1/2~1/3 better than your average seeing... ie.. if you regularly experience 2 arc second seeing, you would essentially want 1 arc sec per pixel... etc.

A few calculations..
480mm FL with 5.4um pixels = 2.32 arcsec/pixel
600mm FL with 5.4um pixels = 1.85 arcsec/pixel
1000mm FL with 5.4um pixels = 1.1 arcsec/pixel
1500mm FL with 5.4um pixels = 0.74 arcsec/pixel
2000mm FL with 5.4um pixels = 0.56 arcsec/pixel - Over sampled

480mm FL with 7.8um pixels = 3.35 arcsec/pixel - Under sampled
600mm FL with 7.8um pixels = 2.68 arcsec/pixel
1000mm FL with 7.8um pixels = 1.61 arcsec/pixel
1500mm FL with 7.8um pixels = 1.07 arcsec/pixel
2000mm FL with 7.8um pixels = 0.8 arcsec/pixel
2500mm FL with 7.8um pixels = 0.64 arcsec/pixel

Now, whilst binning can be employed to effectively double your pixel size, making over sampling less of an issue, you are then halving the image size, which for me, considering I like to get my astro images printed from time to time, becomes a pain in the bum... I didnt pay for an 8.3mp camera so I could take 4.15mp images..

It should be noted, its usually better to over sample than to under sample. oversampling can be a good thing on nights of very good seeing, also certain processing routines (like Deconvolution) seem to like oversampled data...

There are more qualified people than myself who can better explain the ins and outs of sampling etc.. but from what I've seen using a few different cameras with very different pixel sizes in a variety of scopes is this, the closer I get to 1 arcsec/pixel, the sharper the images become..

marki · #29 29-12-2009, 01:29 PM

Alex, from my understanding 2x2 binning will use 4 pixels to do the job of one so your reduction is 4x i.e 8MP becomes 2MP.

Peter if you have a long focal length scope you can always use a reducer with small pixels.

Mark

mill (Martin) · #30 29-12-2009, 01:47 PM

Ok i have just ordered the QHY9 from Theo and should be able to have it in my grubby hands in a couple of weeks.

Tilt (Michael) · #31 29-12-2009, 08:22 PM

Ok, so a QHY8 would be better for scope with a FL of 480mm?

AlexN · #32 29-12-2009, 08:59 PM

Nope, the QHY9 suits a 480mm F/L better... Smaller pixels for smaller scopes, bigger pixels for bigger scopes.

AlexN · #33 29-12-2009, 09:03 PM

Essentially, the KAF8300 (as found in the QHY9) has pixels slightly larger than what you'd like with a 480mm focal length.. 2.32" per pixel isn't bad, but its by no means great... The Kodak KAI-10100 sensor is a great match for the 80mm F/6... it has 4.75 micron pixels... Unfortunately its only available as OSC, and currently only in FLI Proline cameras, SBIG have noted on their website that an STX-10100 is on the cards...

Peter Ward · #34 29-12-2009, 09:37 PM

OSC is a severe limitation if you want to shoot H-Alpha or similar narrow band images: significantly worse QE and resolution.

While mono means more work and cost, the results speak for themselves.

AlexN · #35 29-12-2009, 09:45 PM

Indeed... I struggled with OSC Ha imaging for some time.. Even with 6 hours exposure I could not get a really really clean image of the horse head.. Noise was really hard to control because signal was so hard to attain.. On brighter targets like Eta Carine the OSC camera did ok with Ha, as with M8/M20, but on dimmer targets it was a real pain... Mono is really the way to go if you want to image in narrowband.. OSC can do the job, at the cost of all the hair you pull out along the way..

Tandum (Robin) · #36 29-12-2009, 09:54 PM

Quote:

Originally Posted by Peter Ward

OSC is a severe limitation if you want to shoot H-Alpha or similar narrow band images: significantly worse QE and resolution.

While mono means more work and cost, the results speak for themselves.

Peter, do you have a OSC in your kit?

Hagar (Doug) · #37 29-12-2009, 11:35 PM

An interesting review/comparison of OSC and mono CCD cameras.

http://www.stargazer-observatory.com/mono_vs_osc.html

Written by Dietmar Hager, a brilliant imager.

AlexN · #38 29-12-2009, 11:46 PM

Dietmar definitely knows his stuff.. It would be great to see someone doing the same sort of test with a KAF8300M vs KAF8300C... or KAI-11002M vs KAI-11002C.

Apples vs Apples, Oranges vs Oranges..

I don't know if that would change the results or or make them more conclusive, Just think it would be interesting to see.

RobF (Rob) · #39 29-12-2009, 11:56 PM

Quote:

Originally Posted by Hagar

An interesting review/comparison of OSC and mono CCD cameras.

http://www.stargazer-observatory.com/mono_vs_osc.html

Written by Dietmar Hager, a brilliant imager.

Wise council as always Doug, suggesting people digest Dietmar's observations. In my case I'd like to see some more resolution from QHY9 over my current 450D, but its really sensitivity and flexibility to learn and explore more imaging options I particularly like. Ha seems particularly intruiging and its interesting Dietmar notes you can get close with OSC but mono generally better for Ha.

I guess if we're going too far out on the imaging limb there'll be some great mono QHY9 deals going in 6 months. I only say that partially tongue in cheek knowing you've been down this road before and didn't enjoy all the extra messing around with LRGB.