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Problems with long exposures and pollution...


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Thanks guys! i dont know why i didnt think about trying that before. i still have the dew shield that i used to use with my old C8. im pretty sure i can find a way to make it fit on my newt. and its pretty long too. Something like 10inches or so :(

Cant wait to give it another try :)

and ill probably stick to the iso 800 and 2min subs...

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If it helps, I use ISO 800 and a makeshift dew shield for my 6" Newt. ISO 1600 is way too noisy, and ISO 400 generally too weak. 800 is the best compromise for my 1000D and might be a good starting point for you too.

The dew shield is just a few inches long, and attaches to the end of my Newt via some velcro strips. It's not pretty, but it works!

That's exactly what I do too.

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yea it totally makes sense to me now :)

Since the camera is so close to the telescope entrance, it must capture alot of stray light.

isnt it also true that even the viewfinder on the camera catches unwanted light as well? should i cover that as well with a small black cloth?

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yea it totally makes sense to me now :)

Since the camera is so close to the telescope entrance, it must capture alot of stray light.

isnt it also true that even the viewfinder on the camera catches unwanted light as well? should i cover that as well with a small black cloth?

First part - yes, absolutely. I'm really excited by the prospect of flocking the outer part of the tube since if I can see it, there's reflected light (entering the tube, hitting the tube wall, bouncing off and entering my eyes). I'm thinking that flocking will noticeably improve contrast.

I'm not sure about the viewfinder though, since the mirror would flip up and hence obscure the viewfinder from the chip. I could be corrected though - can anyone else add anything to this? Should we cover viewfinders on astro DSLR's?

Mike

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So here are two examples...

The first one was taken with the Baader Skyglow filter... 12x2min in ISO 400. stacked and messed with levels and curves. (Sorry for the horrible guiding)

The second is taken with my CLS clip and the dew shield installed. 33x2min in ISO 800. Stacked and messed with levels and curves.

Im not sure, but they seem almost the same to me :)

Should i maybe try to take another set with my CLS clip and the new shield but in ISO 400??? Maybe the high ISO is catching way too much city light in the smog??? Thus giving me such bright subs like the one in this thread... It seems like this brightening in the subs is hiding all the details in the images, and thus causing the need for much more subs? (Like what happened with those two hours of subs on M109...)

What do you guys think???

(What do you guys think will happen if i combine both the Clip and the Skyglow filter together???)

post-24989-133877565798_thumb.jpg

post-24989-133877565806_thumb.jpg

Edited by AlexxxAA
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Interesting effect, it looks like something (noise?) has been processed as part of the captured in image, like circular rain :), almost like particles in the atmosphere were visible and caused trails during tracking, is this rotation or some registration artefact? Worse in the second image, awaiting with interest some expert diagnosis.

Edited by nightvision
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Seems you have a lot of co-related noise, all down to sub exposures that are too short. It can produce some funny patterns, almost like a Moire effect at times.

If you want to compare two images it is best if they are essentially the same. 24m at 400 and 66m at 800 are definitely not the same. Whilst I understand the 'messed with levels and curves' comment you should try to post process them both the same way. Try doing the 'best' result and record it as a Photoshop action, then replay the action on the second picture. Be prepared for a shock, identical processing might not give you an identical result.

Dennis

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I'm not sure about the viewfinder though, since the mirror would flip up and hence obscure the viewfinder from the chip. I could be corrected though - can anyone else add anything to this? Should we cover viewfinders on astro DSLR's?

Mike

Yes, absolutley. Light can and does enter via the viewfinder. Canon even provied a little rubber doobrie that replaced the viewfinder eye rubber.

I lost some subs as a transformer had a LED that was shining onto the viewfinder, which leaked onto the sensor.

I now stick some duct tape over the viewfinder. It's one less thing to worry about, TBH.

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Yes, absolutley. Light can and does enter via the viewfinder. Canon even provied a little rubber doobrie that replaced the viewfinder eye rubber.

I lost some subs as a transformer had a LED that was shining onto the viewfinder, which leaked onto the sensor.

I now stick some duct tape over the viewfinder. It's one less thing to worry about, TBH.

*Thank you* Zakalwe,

So >THAT's< what the rubber piece was for :)

I'll use a bit of duct tape too, as you say it's one less thing to worry about.

Best,

Mike

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