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12-12-2010, 04:40 AM   #1
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Focusing Screens K-7 Astronomical

Hi all, just wanted your opinion. I have a K-7 that I intend to use for astrophotography. Focusing can be difficult with faint point sources of light.
Exposure times can be long 30secs or more etc. My question is: What focusing screens do my fellow Pentaxillites suggest for faint astronomical objects????

THX

12-12-2010, 07:57 AM   #2
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You can use a Ronchi screen/knife edge setup

Knife-edge Focusing, Ronchi Astrofocusers, Wide-field adapters, Stellar Technologies International

Or just focus on a bright object like jupiter or venus or sirius to make sure you're focusing on infinity precisely then slew to your DSO
12-12-2010, 05:37 PM   #3
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thx

Hey thanks
The link looks promising
but does not connect with prices and ordering.
I have a mask that I might use more often......
It's got a sort of "Y" pattern on it.
But still a better screen might be good too.........
12-12-2010, 05:51 PM   #4
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OK I've had another look.
Taking out the Ronchi Focuser and replacing with DSLR at 4am in the morning is not an option. It's gotta be with camera in situ hence the focusing screen.


Last edited by Postumus; 12-12-2010 at 05:54 PM. Reason: Typo
12-13-2010, 06:50 AM - 1 Like   #5
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Liveview? (I'm sure there is a good reason you're not using this, though...)
12-13-2010, 12:18 PM - 1 Like   #6
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I hate to be that guy, but the K7 is not Pentax's best camera to use for astrophotography. I own it and a few other bodies and I can assure you that while you'll still be able to do it, you don't know what you're missing unless you use one of the Pentax's that DOESN'T use the Samsung sensor, such as the Kx, Kr or K5. Could you get a hold of one of those?
12-13-2010, 04:51 PM   #7
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I know the K-5 is much better than the K-7 in low light. But even I have a budget. I'll treat myself to a K-5 sometime next year. But in the mean time the question of focusing screens remains as the K-5 and K-7 use the same ones I believe. I still use my ist DL2 even though it's "older" technology.

I hadn't thought about liveview cos I've not really played with it much. Traditionally however I only trust my poor quality vision, above devices!
But will give it a go as soon as the weather clears up.
Thanks for your suggestions..............

Last edited by Postumus; 12-13-2010 at 04:57 PM. Reason: Addition
12-13-2010, 05:59 PM   #8
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I've been focusing astrophotos since 1997. If you mean a focusing screen internal to the camera I can't see how that would help when you are looking at the night sky. I had a K1000 with split ring focus aid, the focus screen was useless in the dark.

What I use is a Bahtinov mask from this company:

Bahtinov Mask by Focus-Mask

I have two, $24.95 for my refractor and $34.95 for my SCT. The smallest one they make >might< even work on a lens or you can make a smaller one from plans.

Unlike ALL methods I tried in the past, the Bahtinov:

1. Tells you the direction to go. No more guessing one way to see if it is right, then having to start over the other way if you guessed off wrong. Think about it, that is how we manually focus cameras during the day. Turning back and forth to find the best focus!

2. Tells you when you are already focused. Other methods require you to unfocus to discover you were already at best focus. I check focus on occasion throughout the night. With the Bahtinov mask if the cross bar is centered I'm done without touching the focusser!

If you are on a tight budget Focus-Mask lets you download their actual layout so you can make your own. But, the black plastic ones they sell are hard to beat.

Once I tried black I never went back to the old way of focusing astrophotos.

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