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Which Barlow for Philips SPC 900?


Dan Watts

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Hi everyone,

I was in the process of finally getting a Philips SPC900 Webcam to start getting into some imaging and after doing some research, realised I also need a decent Barlow to go with it.

I have an Orion XT8:

  • 8" Aperture
  • 1200mm focal Length
  • F5.9

I wondered if anybody could assist with an optimum Balow to use with this webcam and scope - I have seen the Barlows go up to x3, x4, x5 etc.

I know there is a formula to work out the max mag, any help would be great :)

Thank you.

Dan.

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It's a bit more complicated that that. This might be worth a read:

http://www.tanstaafl.co.uk/2012/03/focal-ratio-capture-length-planetary-imaging/

But there are other factors that need taking into account, too. For instance, depending on the seeing and the distance/elevation of a target sometimes it may be possible to use a particular focal length and other times not.

Maximum magnification is not an issue with imaging because the process is different from viewing.

I'd be tempted to try something like the GSO/Revelation 2.5x barlow which is reasonably priced and pretty good for the money. I have an extension that I sometimes put after the barlow which is a kit Skywatcher barlow with the lens removed and that gives me a bit higher multiplication factor -- somewhere between 3x and 3.5x so if you could find something like that as well it would give you a range of options. Once you want to get up to 4x and 5x multiplication, which may well be possible with your scope, I think you really need to be looking at the high quality kit such as the Tele Vue Powermates.

James

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It is probably worth bearing in mind that once you get up to 4x and 5x focal length, keeping the target on the SPC900 sensor means your tracking needs to be pretty good. There's very little margin for error. I don't think I'd want to start out at that point.

James

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Yeah, being a Dob, it will be a case of letting the planet roll across the camera and then stacking the frames thereafter.

Not the easiest method but it can be done...Must make sure I have patience aplenty ;)

I think maybe a x3 or x4 might be a good starting point...I have also read an extension tube might be required to increase the focal range to obtain focus.

Dan.

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I don't find it easy to get objects in the sensor with a 3X Barlow even using GOTO and I have yet to manage a decent capture using my dob even with a 2X. I decided to give up trying again until the clocks go back as I find my patience runs out far quicker in the wee hours than it does at 10pm! Good luck!!

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