Tele vue Pronto for wide-field imaging?

[davidrandell]

Hi Everybody,

This is my first post to this forum.

I'm interested in getting into wide-field astro imaging (CCD or DSLR) and looking looking for suggestions. I have current budget of ~£1,400 to upgrade, replace or add to current items of kit.

By way of background to my questions: the equatorial mount I have is an early example of the green livery Vixen GP mount with motorised RA and DEC drives (both Vixen MT-1 motors) and a equally venerable 3rd-party hand controller modified with an autoguider ST-4 port. This is a non-GOTO setup. I also have a 70mm f=480mm TV Pronto and a dedicated TV 1.08x field flattener for imaging full frame (though the Nikon D50 I have restricts this to the APS format). As to other imaging related kit: I have a 2" photographic Lumicon Minus Violet filter inhertied from my film days and a 80mm f/5 refractor that could be used as a guide scope. As to experience in astrophotography, this is limited. I've done a bit using film (35mm format) and latterly with the D50. On the image processing front though I am a Computer Scientist working in digitised histological image analysis so am very familiar with image capture methods and processing low-level images.

What I am not clear about is to what extent the Pronto with its ED doublet (and residual secondary spectrum) limits what can be achieved compared with an well corrected APO using the same focal length. Also if  looking at a APO, should I aim for, e.g. the Altair Astro 80mm f/6 or the 102mm f/7 APO triplets? In fact some posts about imaging seem to prioritise the importance of the mount over the scope, while some prioritise a CCD over a DSLR and a larger aperture scope, other things being equal. So these are the sort of questions running through my mind...

For a start has anyone directly compared images from the 70mm f/6.9 Pronto with an APO of the same focal length?  I know Olly Penrice posts here and has a Pronto, so if you are reading this Olly I would be be particularly interested in your thoughts on this).

Many thanks,
David Randell
 

[ChrisLX200]

The Pronto is a respectable scope in its own right, especially if you have the optional flattener for it. I have one (without flattener) but I used it mainly as a guidescope, but also for some lunar imaging where it produced very sharp images. If I didn't have a variety of other OTAs to use I would certainly have tried it for DSOs too.

ChrisH

[ollypenrice]

Hi David. I do have a Pronto but have never imaged with it. I bought it for widefield visual use at which it excels. However, I have imaged with a Mk1 'Pearl River' Genesis, I think late eighties, and of a similar design generation to the Pronto. I strongly suspect that, at this pre-CCD, pre-digital time, correction into the blue was not the priority that it is today. The Genesis did get me started but blue stars bloated and this might also apply to the Pronto. On bright targets (for which I don't use it) there is violet fringing even at the eyepiece.

The focuser is up to the job and the R and P beats all those infuriating Crayfords that plague budget scopes. By attaching a simple lever or wand to the single speed knob you can make it digital-imaging friendly. If you went down the CCD route it would probably be great for narrowband where colour correction is not needed.

I have tested some of the Altair triplets but these were sent to me expressly for review and it breaches the forum code to discuss them on the open site. Feel free to write to me on my regular email account which I'll attach via PM. It's on my website as well. I think my review is also on the AA website. (While many people think reviewers are in the hands of the advertizers I can promise you that neither Steve Richards nor I will agree with this. We certainly aren't.)

I am firmly in the 'Mount-Camera-Optics camp.' You must, must, build from the mount upwards. You can have any optics you like but if you can't guide them you can't image at all seriously. GoTo is not essential but it is a time saver, a massive time saver, and any UK imager will tell you that wasting it is a nightmare because there isn't enough of it! However, I don't always agree with the idea that you must have mount overkill. Have it if you can afford it but if you are using a small refractor (a wonderful way to image) then there is no need whatever to prefer an HEQ6 over an HEQ5. The 'five' is fine.

You already have a camera, you already have a scope. They might not be perfect but you have them. Given how much there is to learn and to beat into submission (this stuff rarely 'just works...') my inclintion would be to go for a modern, fully featured mount and get it guiding.

Best of luck,

Olly

[davidrandell]

Thanks for the useful replies Chris and Olly. I'm going to seriously re-think this one. I get Olly's point about the importance of building from the mount upwards and ease of use GoTo would provide especially if imaging imaging under UK skies and tragetting faint objects and using a relatively small sized sensor used in entry level CCD cameras. Using the Pronto for narrow-band imaging is an interesting idea. The Pronto example I have stars test well and can handle a high magnification and the Nikon D50 seems well-suited for astro DSLR imaging. I do see violet colour fringing though when used visually with well-corrected eyepieces so would expect bloated star images as a result when imaging. So I'm going to do a bit of research now on suitable mounts and the HEQ5 seems a good place to start.

Regards,

David R