DBK21 DBK31 and what is possible with a Dob

[DB]

I have a 12.5" truss Newtonian and am keen to get some shots of Jupiter. I have a tracking platform on loan that works reasonably well, however, I find it a bit of a challenge to get the planets centred (the platform introduces a bit of whiplash). I am trying to decide between the DBK21 and 31.

2 questions:
1. Is it possible to get reasonable planetary images on a platform as opposed to a mount?
2. Would the 31 give me a bit more extra field and therefore make it easier to capture a sequence for processing?

Many thanks!

regards

David

[acropolite (Phil)]

1. Is it possible to get reasonable planetary images on a platform as opposed to a mount?

It's possible, Mike has written a how to on this subject and produced some amazing results using a DOB/EQ platform. Hopefully Mike see this thread and respond.

[Matty P (Matt)]

Hi David,

The DBK21 has a smaller chip but allows you to capture up to 60fps. The DBK31 has a larger chip but only allows to capture up to 30fps.

I'm not sure if the larger chip would make that much difference for planetary imaging so I think the DBK21 is the way to go.

Please correct me if I am wrong.

[DB]

Thanks Matty

I looked at some of the older threads and picked up on the advantages of monochrome (plus filter wheels) compared with the DBK in terms of resolution. My truss is now set so that a CCD camera (MallinCam) can be focused when the focuser (Feathertouch) is almost fully racked in, and the eyepieces when almost fully racked out. My concern is that adding a filter wheel will mean that the arrangement will not accommodate the eyepieces/MallinCam/DMK on the same set of poles, as I will need to rack the focuser in a further 15-20mm beyond where is it now in focus with the webcam and I don't have that amount of travel left. Is this correct?

David

[iceman (Mike)]

Hi David

I'm not sure about the focal point - you'll just have to try it and see.

There is absolutely no reason you can't do imaging on a platform - you don't NEED an EQ mount, as long as you have fairly tracking via your mount.

All of my images during 2006 were taken with my 10" dob on a tracking platform. An article during that time is here: Planetary Imaging and Image Processing, and my image gallery from 2006 is here: Jupiter 2006

The EQ platform has to be accurate enough to keep Jupiter in the field of view of the camera at long focal lengths - so it will help if you have some fine adjustment controls. My platform had one knob to speed up or slow down (in RA). No dec adjustments.

The DMK31, with the bigger chip, will help you to keep the planet in the field of view, but my experiences when comparing the DMK21 with the Astrovid Voyager X, had me leaning towards the DMK21 in terms of sensitivity (the DMK31 uses the same chip as the Astrovid Voyager X).

But it will still be possible to capture great images with the DMK31 - even as a planetary camera. And if it makes it less frustrating keeping the planet on the FOV, then go for it!

I was very happy to replace my EQ platform with an EQ mount - it just made very long focal length planetary imaging soooo much easier to do, but imaging with a platform is certainly possible and you can get some very good results. I did it for about 18 months before going to an EQ mount.

[DB]

Mike

Thanks for that. I am a bit wary of buying the DMK and filters to find that they throw everything else out. I can't figure out how anyone could have an arrangement where both the DMK + filter wheel and the eyepieces could be focused on a standard focuser. I have a Feathertouch (2020BCR) 2" and need all the travel with a CCD (at one end) and the eypieces at the other. Do people use an extension tube to move the eyepieces out when they add in a filter wheel or just live with not being able to do both or have more focuser travel?

regards

David

[darrellx (Darrell)]

David
I am in the same position as you, and have looked forward to some of the responses from this thread. I have recently purchased a DMK, and to date, I am very pleased with the shots. Like you, I am reluctant to purchase a filter wheel and filters if I have trouble with focus. I have a crayford, with only 18mm of inward travel remaining. The filter wheels I have looked at require between 20 and 30mm of inward travel to focus.
From what I have read, it seems that most people use a barlow in the setup to achieve focus. But I am still a little confused and suspicious. It seems that "telescope-barlow-filterwheel.." is the way to go. I have also seen a suggestion that "telescope-filterwheel-barlow.." will also work.
I am wondering if this is a typical setup.
Darrell

[iceman (Mike)]

Hi Darrell, to IceInSpace.

I can't bring my DMK to focus at prime focus in my 12" newt - but with a 2x, 3x or higher barlow (I use a 5x powermate mostly), it comes to focus fine.

With a DMK + filterwheel at prime focus, it can't come to focus either. But again with a barlow, it will come to focus fine.

If you're doing lunar or planetary imaging with it, it's rare that you'd want to use the DMK without a barlow of some sort, so I don't expect you'll have a problem.

[DB]

Mike

Thanks for the clarification. Do you know how much travel a 2X Barlow adds? Also, are you aware of any 'low profile' filter wheels that minimize the additional path imposed?

I read your analysis of the pros and cons of color versus monochrome/fw setups and can see how the color CCD design has less resolution. Are there any comparative photos of Jupiter or Saturn with color versus monochrome taken at the same time? I have seen some nice images with a ToUCam but I guess it is hard to know what it might have been like on a monochrome camera.

Darrell, I'd be interested to hear how you get on.

regards

David