Choosing a DMK camera...

[MarkAndLeanne]

...or how to start a long argument on a forum

We're looking to get hold of one of these cameras, because all the people who 'know stuff' say we should. The question is which one? If money were no object (which of course it is!), which is the better option in the range?

We've decided that Mono + Filter Wheel + LRGB seems to be the best way to go, but there are still choices to make:

1) USB2 or firewire? My belief is that firewire gives a slightly faster transfer rate in the real world (I know the spec is similar) and so would be the better option as our laptop has a FW port.

2) Which resolution? The DMK21 seems most popular, and offers a higher frame rate (60fps) along with larger physical pixels than the 31/41. However, 640x480 sounds like small images, so is it worth trading frame rate for resolution and moving up to the DMK31 (30fps) with its smaller pixels? Further, the DMK41 has the same pixels as the DMK31 (just more of them), but a slower frame rate (15fps), presumably due to the larger data capture in the larger frames.

To complicate the problem, we have a digital photo frame at 800x480 resolution, and it would be nice to have finished images that we could crop down to fit rather than having to enlarge them?

Gut feeling is the 21 or 31, as 15fps seems a bit slow, and the extra resolution of the 41 is marginal. What do you reckon?

:? :? :?

[SteveL]

I believe (and I know I`ll get corrected by those who "know stuff" if I am wrong!) but the firewire versions require an external power source, but the USB ones are powered from the USB cable/socket.

[jcm]

I believe (and I know I`ll get corrected by those who "know stuff" if I am wrong!) but the firewire versions require an external power source, but the USB ones are powered from the USB cable/socket.

Yep , if you use the "tiny" firewire port on a laptop you need a special cable which allows the connection of a 12v power supply.

If you add a PC card to your laptop to add full size firewire sockets you need a card which has a 12v power socket.

Link for power 6 pin to 4 pin cable b- http://www.usbnow.co.uk/Cables-Firewire_Cables/c1_3/index.html?gclid=CIitreGS_JMCFQzklAod8RixWA

Link for PC card - http://www.maplin.co.uk/module.aspx?ModuleNo=47103&doy=17m6#overview

John

[Trevor]

Mark/Lee

Ed has the DMK USB and I have the Firewire version, if your laptop has the 4 pin firewire connection you can get a powered lead from Bern, with the DMK 21AU04 you can easily get 60 frames per second on Lunar imaging, however if using one of the higher resolution cameras that have a maximum of 15fps you will struggle to get a fast frame rate for planetary imaging you will be down to something like 7.5fps or lower, I was shooting Saturn and could not get above 30fps for lum and was down to 7.5fps for the blue channel, I would recommend go for the DMK 21AU04 mono

Example of image size:

(click to enlarge)

With the Lunar imaging it is easy to resample the images in Registax.

Example: click the image then click again.

(click to enlarge)

[MarkAndLeanne]

Thanks guys. Still a toss-up between the USB and FW; will give that a bit more thought, but considering that we've got a 12V power tank for the mount, the FW is still an option.

Trev - cheers for the piccies. Hadn't really got as far as realising that if you shoot 3 channel colour as 3 mono with filters, you are effectively increasing the resolution of the camera. Certainly, looking at your Theophilis shot, at full res of 1600x1200, it's as good as we could ever hope to achieve! Put a few things into perspective, that's for sure!

You know stuff too!

Mark & Lea

[MrEd]

Hi Guys

You can get the camera in colour and Raw versions as well as mono.

If you are beggining imaging on the solar system i reccomend a colour webcam

until you can master the basics. Jumping straight into mono has

a steep learning curve.

Also frames are very severly hampered with filters with my 8" i was down to

3fps on the blue channel imaging Saturn.

So my advice Master a colour webcam, If you want a DMK now go for the RAW colour vesion. The smaller one is the best for frames on all subjects the other 2 sizes are better on lunar and solar work.

As for the USB2 Firewire buisness you still get the same frames from both,

but USB2 is more automated and easier to use in the field or other peoples scopes. (but then again thats a tad bias )

Hope that helps

Ed