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  #21  
Old 15-09-2013, 04:49 PM
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Quote:
Originally Posted by Peter.M View Post
Using the numbers you provide, newt spits out a 100% illuminated area of 0mm which may explain what you see. Your tube inside diameter is distance A on your diagram times 2 so 300mm. Then all you need to do is make sure all of the other values in newt sum to be the 144mm of extra distance to the focal plane and it should give you the same numbers.

What you may be seeing with the qhy8 is vignetting of the 75% rays in the corners of the chip. Though I am not familiar with that.
Hi Peter,

I'm probably using different values but I get a 7mm illuminated circle.
screenshots attached.
pls let me know which one's off??

what I did notice is that the 22mm distance I have for the focuser base to the inside of the scope reduces the illuminated area.
so if I move the focuser inward by 22mm, it doubles the area with the same secondary.
I would of course have to move the primary down else i'll have to use extension tubes.

what is the end result of a larger circle? any change in contrast or sensitivity, as in more light??

Alistair
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  #22  
Old 15-09-2013, 04:52 PM
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Quote:
Originally Posted by gregbradley View Post
Nice looking scope. Newts typically need a coma corrector. Do you have one of those? MPCC is common one used.

Sounds like you've got the CCDs worked out there. Its just a matter of going through the pluses and minuses of each and which match your intended main interest in imaging. CCD calculator at New Astronomy Press (its free) gives you a simulation of the view of different deep sky objects with different cameras on the same scope. That may help with the decision process.

ST8300 is proven.

SXV694 seems to be a strong performer but a bit smaller FOV which might be good for galaxy images but not so good for wider objects. Its also very modern, has good electronics, its a Sony sensor. Mike S likes his and Rally's few images posted so far are impressive with a similar setup. It also requires a smaller corrected image circle not that KAF8300 requires a large one either. KAF8300 is about 58% QE and not sure what its QE at Ha is. 694 is 77% and 66% at Ha which is one of the highest around.

ST10 is another strong performer plus it has self guide (I presume). That is good for LRGB not so much for Ha.

Greg.
Thanks Greg,

Yep I'm using the mpcc mark3 which has an M48 opening as opposed to the T2 of the mark 2.

what is the next medium format chip up from the 694/8300?
I do like a large FOV, and the qhy8/8l would have been perfect if it were mono.
i might have to give that a shot to remove a qhy8's CFA.
apparently dichloromethane removes the CFA of a nikon D40 easily and that's the same sensor used in the qhy8.

Cheers
Alistair
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  #23  
Old 15-09-2013, 05:35 PM
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what is the next medium format chip up from the 694/8300?
I do like a large FOV, and the qhy8/8l would have been perfect if it were mono.
i might have to give that a shot to remove a qhy8's CFA.
apparently dichloromethane removes the CFA of a nikon D40 easily and that's the same sensor used in the qhy8.

Cheers
Alistair[/QUOTE]

I guess the next size chip up from KAF8300 would be the DSLR equivalent of an APSc sensor 26x15mm. The KAF6303E I think is around this size. Not much really. Next size really is full frame 35mm or the KAI11002 chip or its cousins the KAI29050 (29mp). There is a Sony 14mp CCD in one of the QHY's.

The usual cameras are:

KAF8300 - FLI, Apogee, SBIG, QSI, Atik, Starlight Express, QHY, Moravian
KAI11002 FLI, Apogee, SBIG, Atik (cheapest), Starlight Express (I think).
KAF6303 (usually expensive) same as above except not sure about SX or Atik.

There is also a KAI 8050 and a KAI10100 (one shot colour only).

I think though for the price point and type of scope it boils down to a KAF8300 camera or a Sony 694 camera. Perhaps the ST10 or a 2nd hand STL11. But STL11 is a large sensor and it will cause problems with vignetting, you really need a larger focuser and larger corrected image circle (something like 44mm diagonal).

I think it boils down to really ST8300 or its equivalent or a SX694 myself and either will produce great images with that Newt.

That chemical sounds really nasty. I would take lots of precautions handling that.

Greg.
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  #24  
Old 16-09-2013, 11:00 AM
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Spoke to the local sbig retailer, I might go with the stf8300m and use a sx filter wheel with the TS9OAG.
need to figure out if all of this would fit together and i'll have to change the coma corrector as well as the filter wheel depth is 29mm.
the sbig has a T thread, is this the same as M48?

Cheers
Alistair
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  #25  
Old 16-09-2013, 11:12 AM
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Alistair,
A T thread is M42 x 0.75, much smaller diamete than the M48 filter thread.
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  #26  
Old 16-09-2013, 11:33 AM
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Originally Posted by Merlin66 View Post
Alistair,
A T thread is M42 x 0.75, much smaller diamete than the M48 filter thread.
Thanks Ken,
always confuses me.
is the T2 the same as a T?
isn't M48 the same as a 2inch nosepiece?

in short, which adaptor will I need from SX to fit the sbig's T thread?
will the T2 male work?

http://www.sxccd.com/sx-usb-filter-wheel

Thanks
Alistair
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  #27  
Old 16-09-2013, 01:02 PM
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normally a T2 adaptor is a camera adaptor which has a T thread element then an insert (held by three grub screws) to match the camera flange - hence the two part "T2"
The M48mm filter thread is the normal filter thread for 2" eyepieces etc.
According to the SX datasheet, you can specify both the inlet and outlet threads....yes, the "T2 male" would probably be the one needed to fit the Sbig camera.
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  #28  
Old 16-09-2013, 08:28 PM
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hi

anyone with an stf8300m know if it has single or dual stage cooling?
Peter from ATS wasnt too sure but did say that it can go to -20 in summer.
the qhy9 seems to have better cooling and a heated window although I'm not too sure if that alone should be the basis for a decision.
the qhy shutter is also slower from other threads here.

any stf owners able to chime in on the cooling performance?

thanks
Alistair
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  #29  
Old 16-09-2013, 09:22 PM
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I have a FLI ML8300 and it cools heavily but I must say the chip looks totally perfect from -15C onwards.

Greg.
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  #30  
Old 18-09-2013, 10:41 AM
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Hi,

Almost ordered the stf8300m, but came across the G2-8300's cooling performance which is apparently 50 below ambient as opposed to the stf's 40 below.
is this significant enough?
Peter W mentioned that the sbig can go to -20 on 20deg nights. but that'd be pushing it hard.
can any stf owners comment on the cooling and what they normally reach?

Thanks
Alistair
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  #31  
Old 18-09-2013, 04:52 PM
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Quote:
Originally Posted by alistairsam View Post
Hi,

Almost ordered the stf8300m, but came across the G2-8300's cooling performance which is apparently 50 below ambient as opposed to the stf's 40 below.
is this significant enough?
Peter W mentioned that the sbig can go to -20 on 20deg nights. but that'd be pushing it hard.
can any stf owners comment on the cooling and what they normally reach?

Thanks
Alistair
It's not just about cooling performance. SBIG are rather conservative with their cooling specs....(they have to guarantee their published delta T )

A little known fact is they also have a patent on holding CCD chamber temp stability to around 1/100th. The end result is a much cleaner and consistent dark calibration... which far outweighs an albeit higher but inconsistent delta-T IMHO.
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  #32  
Old 18-09-2013, 05:39 PM
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+1 to SBIG cameras, I have the STT8300, if cooling is your major concern, have you considered the STT line? That said, -20 C for an 8300 sensor should be sufficient, I don't bother running mine much below that even though I can push it further with ease. Peter is spot on, temperature stability is of higher priority, stable darks can deal with the noise.
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  #33  
Old 18-09-2013, 05:42 PM
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Alistair,

Delta 40C gets rid of 99.2% of the original dark noise at ambient
Delta 50C gets rid of 99.7% of the original dark noise at ambient

Its really a trivial difference, to get carried away by it !

Is this important to you ?
Do you have all the other sources of noise under control to this extent ?
Can you be assured that all your subs are within that degree of perfect focus, what about your guiding and tracking accuracy, what about collimation and coma or tilt etc . . .

Camera integration and other features will far outweigh that last 0.5% of dark noise.

From a Dark's management perspective its easier if you hold a consistent temperature across the seasons (or maybe just two) rather than going for maximum possible cooling - because you will then need to create, manage and maintain multiple Dark's libraries
So that usually means not running the camera at 100% of cooling capacity in any event - but something that works in Summer and winter and probably never exceeds maybe 90-95% on the hottest of nights.

As stated, better to have accurate and consistent Darks than necessarily the coldest possible camera.
If you are really worried about this, then you need to upgrade to the next class (or three) of equipment !!!
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  #34  
Old 18-09-2013, 06:42 PM
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Hi,

Thanks for all the info.
you're right, there are several other factors to get right, and I'll probably set it at -16 or so most of the time. thats why i thought i'd ask first.

the STT has some serious cooling but it would blow the budget.
i'm happy with the stf8300m and an sx 7 position wheel.
the lodestar is arriving tmrw, now to order the rest and fix my image circle issues.

silly question perhaps, if i point to a full moon and keep a paper at the ccd focal plane, would i be able to see the illuminated circle?

cheers
Alistair
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