#21  
Old 23-01-2010, 05:16 PM
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Whoeww Marc ! They are shockers LOL
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  #22  
Old 23-01-2010, 06:59 PM
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Marc and Alex

thanks for your time on this.

There are a few interesting ones there Marc - might make a good thread actually. We can call it Bring Out Your Dead. I have a few more to add believe me.

Looking at Marc's examples it seems my shot is closest to the fourth.

If I'm right, its a result of placing the MPCC too close to the focal plane. Happily that matches Alex's diagnosis.

I am having a motor fitted to the focuser in the next week or 2 so I'll have the Bintel boys check my collimation. And I agree that the polar alignment wasn't perfect which shouldn't be too hard to sort next time I am outside (damn clouds!).

I'll report back when I make some changes with the spacing.

Alex, on the FW, I'll email your fellow to see what he can do about an adapter and also contact SBIG direct. The yard certainly isn't big enough to satisfy the desire to have burn with the new vehicle as it is.

Pete
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  #23  
Old 23-01-2010, 07:11 PM
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Quote:
Originally Posted by AlexN View Post
Marc - I dont think its field rotation, as the direction of the star elongation seems to point from the outter edge of the field, into the center...
You're absolutely right... Coma... The thumbnail is clearly labeled corner left. I misread it and thought the elongation was not in the direction of the guide star but aligned with the periphery. When Pete confirmed it in his last post after I posed some shots I went back to the shot thinking "what are you guys smokin' ?...." then looking more carefuly realised I'm the one who needs help
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Old 23-01-2010, 08:26 PM
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Not to worry Marc - I do that ALLLLL the time... Misread/Misinterpret whats been said.. Usually I put my foot a lot further in my mouth though haha

In any case - at least its sorted and hopefully with his new spacer, Pete will see nice round stars!

Well... I gotta go... I have a date with some of the nicest looking seeing brisbane has had in a few months... just shooting darks/flats while the moon is up then its off to the target for some quality photon snatching time!! YAY for ME!
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Old 28-01-2010, 09:59 AM
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Nice examples Marc of what can go wrong. Very helpful explanations.

Quote:
Originally Posted by multiweb View Post
Here's a couple of shots and my understanding of what's going on as I eventually fixed it.

1_ obviously field rotation. Everything rotates in reference to the guide star in this case in the keyhole vicinity. (10min exposures). Crisp arc lines. No coma, just field rotation. Combination of field rotation + coma makes stars on the edges look like squares. Still digging out an old tarantula shot. (that's why I said it's a bad choice to test)

2_ Over-correction. MPCC is too far. Stars are bright from the edge blurring inwards (inverted comet). T shape on an ED80 is more pronounced the further out you are.

3_ Collimation. Your field is like a horse saddle. Some of it is perfect some of it is worse. No uniformity. Primary/secondary/focuser axis offset.

4_ Coma (under correction). Stars are bright from the center blurring outwards (comet shape)
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Old 04-02-2010, 09:17 PM
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Originally Posted by AlexN View Post
I'm using an FLI CFW 2-7 7 position 2" filter wheel... It required me to also buy the FLI AD-2 adapter, that allows the use of the FLI CFW with T-thread based cameras..
Out of interest Alex, where did you pick up your CFW 2 - 7?

Pete
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  #27  
Old 04-02-2010, 09:41 PM
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Bought it straight from FLI Pete... It cost $995 USD + 100USD for the adapter between the ST8300 and the CFW (FLI Part no: AD-2) and $25US expedited shipping with UPS.

$1120 USD total, I paid $194 import duty/GST through customs once it got here.. All up it was $1436AU at the exchange rate on the day of purchase, including the GST customs duties etc..

Wouldn't have it any other way! The FLI CFW is superb... its quiet, its very very accurate, repeatability is spot on... The only downside is the cost of 50mm unmounted filters... My NB filter set cost me $1850AUD.. I really wanted the 3nm Astrodon's but they were $1200AUD per filter...

The LRGB filters I managed to pick up 2nd hand off the forums for $375 - A bargain considering they are $895USD new..

The Baader LRGB / SII Ha OIII filters in the 36mm size for the new SBIG ST8300 CFW are actually very affordable... Much cheaper than mine in comparison...
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Old 05-02-2010, 07:12 AM
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Thanks Alex

I have been waiting for some news from SBIG on thier adapter. It looks like they have the 36mm wheel sorted but the adapter for the 50mm remains a mystery.

I have a set of unmounted 50mm LRGB filters which I picked up with the camera. I also have mounted Ha and OIII filters. The FLI site suggests that the CFW 2-7 wheel will take both but I've sent an email off just to make sure.

I'd still prefer the SBIG wheel as it cuts 2 cables out of the equation (USB and power). With all this rotten Sydney weather I am not in a tearing hurry - even though I am keen to take it out for a test drive now.

Out of interest, what spacing do you have with your MPCC?

Pete
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Old 05-02-2010, 11:35 AM
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for the MPCC I got a custom made adapter that goes between the CFW and the MPCC. Its 16.3mm long. This takes into account the width of the filters and their affect on the optical distance between the MPCC and the sensor. It cost me $200 AUD from precise parts in the USA..

Ashley at Precise parts would be able to make you an adapter to go between the ST8300 and the STL FW8 no worries.. Send him and email and he'll do up a quote.. . You don't need to know the specifics of the adapter required, just tell him "I need an adapter to attache the T-Threaded ST8300 to the SBIG FW8 filter wheel" He has technical drawings of all the latest gear, knows the setups and will get back to you within 24hours with a price...

Had I realised that at the time I probably would have bought an FW8... As you say, it runs of an I2C cable that plugs straight into the ST8300, the FLI wheel requires its own USB and 12v power.
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  #30  
Old 05-02-2010, 11:55 AM
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Email sent - thanks Alex.

Still cloudy here in Sydney of course - will be worse when the gear arrives!

Pete
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  #31  
Old 05-02-2010, 12:28 PM
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You might be lucky Pete...

I got the CFW about 2 weeks before the camera showed up.. My camera landed in australia on the 24th of December (Sorry kiddies, no playing outside on Christmas day... Its raining, and its my fault! ) It rained from the 24th to the 3rd of Jan, Then the camera arrived on the 4th of January. (The day I started back at work!! ) Luckily for me, it was still clear that friday/saturday night.. I went out bush and got first light on the first weekend I had it!

Fingers crossed you get the same luck!
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