DMK 1st light (frivolous!)

[ollypenrice]

Well, to my amazement I managed to get the DMK to talk to Registax and take an AVI file. I felt like savouring the pleasures of lunar imaging so I captured a small detail from a relief map in the kitchen using the Pronto.

How silly is that? But I needed to put in a bid for POW, eh?

Olly

[brianb]

[martin_h]

[BlueAstra]

OK, you've forced me. Friday night while setting up for a moon session, I put the DMK on Betelgeuse to focus, then on a whim swung it round to the Orion Nebula for a single shot (6s). Here they are to add to the frivolous DMK collection!

(Not sure why I focus on a star for the moon, I always end up adjusting it. S'pose it puts me in the right ballpark!)

[ollypenrice]

Nah, my Barcelonette is gonna WIPE your Bahtinov for POW, Blue Astro, just you wait...

But tell me, ye planetary sorcerers and gurus, how DO you focus these things accurately with their dancing jittery images and no FWHM? Can you use a Bahtinov on one of the Jovian moons for example? I need to look into all this mystery.

Thanks also to Martin, the supplier of this fine little pea sized camera.

Olly

[brianb]

how DO you focus these things accurately with their dancing jittery images and no FWHM?

It's more of an art than a science. And, like most such things, it takes skill and practice.

Try turning up the gain so you can get a shorter exposure time - that reduces the seeing effects & makes it easier to focus. When you've got somewhere close, reduce gamma to increase the apparent contrast, again this helps you achieve an accurate focus. Don't forget to set the gain & gamma back to sane levels before making the actual capture.

[brianb]

I don't know about using a focusing mask on a Jovian moon - at the sort of image scale typically used in planetary imaging, they're not exactly points. But a nearby star will do. Try to find one fairly near the target image, as optics & focusers can shift slightly when the orientation with respect to gravity is changed - especially systems with primary mirror focusing (SCTs, Maks etc). Meridian flips will almost certainly require refocusing whatever the optical tube assembly consists of.

[ollypenrice]

I don't know about using a focusing mask on a Jovian moon - at the sort of image scale typically used in planetary imaging, they're not exactly points. But a nearby star will do. Try to find one fairly near the target image, as optics & focusers can shift slightly when the orientation with respect to gravity is changed - especially systems with primary mirror focusing (SCTs, Maks etc). Meridian flips will almost certainly require refocusing whatever the optical tube assembly consists of.

Thanks Brian, all duly noted. I thought there would be some magic software around to see to this but a mask on a nearby star sounds like a good place to start. I do have one for the SCT and also a Crayford.

Should I start with a 2x Barlow? Eek, five metres of focal length. I think a metre's a lot in DS.

Olly

[riklaunim]

Focusing with DMK or other planetary camera on high framerate doesn't needs bahtinov mask that much. Focusing while looking on the live view should do. But for longer exposition like methane band or DS imaging I use Bahtinov to focus the setup without problems.

2x Barlow with a f/10 SCT will give you optimal resolution of the scope to the camera - for planetary/lunary imaging (and small planetary nebulas). For other DS you need shorter focal length to see more and for it to be brighter.

[brianb]

Should I start with a 2x Barlow? Eek, five metres of focal length.

Depends on what the seeing's like ... The DMK41 has small pixel pitch (4.65 microns) and doesn't need as much focal length as some cameras to get the same resolution in terms of arc secs per pixel. Even in perfect seeing there's no point in going much past f/25. f/15 to f/20 is probably a good place to start in reasonable conditions, but with a medium/large SCT you can get a pretty decent image even at prime focus.

[ollypenrice]

More thanks.

Small planetary nebulae?? Hey I hadn't thought of that! very exciting...

Oh, one more thing. Do I use a UV/IR cut filter with the DMK21?

Olly

[brianb]

Do I use a UV/IR cut filter with the DMK21?

Not if you're imaging in the ultraviolet or infrared ... but otherwise it's a Good Move. Tricolour seperation filter sets usually have UV & IR blocking built in.

What I do with my DMKs is have a clear glass "filter" (Astronomik Klar) screwed permanently into the end of the camera nosepiece to help keep dust off the sensor.

[Shibby]

Nicely captured object! I've done a little reading and have discovered that it is locatede in the Ubaye constellation and measures some 2x10e-13 lightyears across.

[ollypenrice]

Nicely captured object! I've done a little reading and have discovered that it is locatede in the Ubaye constellation and measures some 2x10e-13 lightyears across.

Quite right Shibby, not a lot of people know that and it was entirely overlooked for POW which is a scandal in my view.

Olly

[BlueAstra]

For Jupiter I use the mask on a nearby star to focus with the gain, etc turned full up. I have also managed to do this with the moons of Jupiter. Back on target I adjust the gain to put the peak at 50% (yellow marker). I readjust the gain for the R, G, B runs so the peak is in the same place. You then take at least one imaging run with the mask still in place before you realise you left it on!

I also use a star & mask for the moon, but its never quite right and I end up refocussing. I guess the moon isn't at infinity! The image turbulence makes it quite difficult so I usually try a few runs at slightly different focus and pick the best after processing.

I find IC capture sometimes a little flakey, with at least one crash during a session. Sometimes I can recover by closing the programme, sometimes I need to reboot. There is another capture programme, Lucam, which is supposed to be better, but its not free.

[ollypenrice]

Thanks BA, all great info.

Olly