Imaging on a dobsonian

[britchall]

Hi, another newbie deciding which scope to buy. I'm leaning towards the Skywatcher 200p dob after reading the advice on here as I value observation more than imaging. Just wondering how long a target at 200x would stay in view on said scope? Also what is achievable as far as web cam imaging of the planets is concerned?

Any feedback will be much appreciated!

[rowan46]

I can't comment on the target time but webcamming with a dob is possible, Last year on this site I saw an image taken of the iss taken with a webcam and dob. Now admittedly he was immensely skillful. but a planet is much easier. in short; its doable with practice. By the way welcome to the site

[britchall]

Thanks! Some web cams can do 90 frames a second (not sure if the quality suffers), so it must be possible if you can keep the target in shot for 20 secs or so. I'm not expecting to much, but would be nice to have some pics showing Saturns rings and some banding on Jupiter!

[rowan46]

the cheapest best webcam for planetary work , they also do the eyepiece adaptor which you will need Cheap Philips SPC880 webcam - 49269 - discounts & offers

[britchall]

That looks like the one to get, as I'm student and on a limited budget. Guessing I'll need a Barlow aswell?

[garyc]

I'm new here, but I just bought two of those cams from Morgan - I just need a telescope to go with them...

I'd assumed from what I read here and elsewhere that a Dob would not be ideal for imaging. Just how do you go about tracking an object at all with them - are you just manhandling the tube and nudging it against the friction of the mount (requiring some dexterity I'd guess to track both alt and az). I don't see any handy wheel on flexible tubes like those on a eq mount for instance.

We've also got a wobbly uneven patio - is a dob on castors really suitable for this and 'off-roading' onto grass?

[rowan46]

I didn't know the dob was on castors but essentially you are right you have to manhandle the dob to manually track the object. It takes a bit of skill and practice but many dob owners do it, most dob owners find them very intuitive. oh by the way this is the most recommended barlow on the site. I don't use a barlow myself but people I trust on here swear that for the price they are the best Tal - Tal 2x and 3x Barlows

[John]

Simple planetary and lunar photography with webcams can be done with undriven dobs but tracking is very challenging - a webcam is the equivalent of a 6mm eyepiece I think so a small field of view to start with. Barlow it and you have a real challenge on your hands.

It can be done but even a simple EQ mount driven on just the RA axis makes it so much easier.

With the undriven dobs tracking is indeed achieved by careful nudging. It's surprising how you get used to it for visual work but can be highly frustrating for imaging.

[Manok101]

If you have a motorized dob is it possible?

[rowan46]

If you have a motorized dob is it possible?

yes its possible its possible even undriven but its very difficult

[Moonshane]

I once timed Jupiter across my scope at 145x and it took a full minute from one side of the field to the other. I am not an imager but I suspect with a fast scope like the one you suggest you would really be best advised keeping the target in the central section of the view as this is where the image is sharper.

you can make a dob tracker for not much money if you have some DIY skills - google equatorial platform.

[todd8137]

the dobs are great after a few nights out the tracking is easy as for photo depends on the ep some timesthings wizz by, and others times a bit slower but wil time a few things dif ep and post ya the results

[DrNeb]

Very interesting.

moving the dob left to right seems quite a chore to be honest for me, it's very stiff! i've loosened the bolt consderably to try and counter it but to no avail. i reckon if i was going to try imaging with it for lunar and planets i'd probably have to mod it.

[garyc]

Oh wow. Equitorial platforms. Something I'd never heard of before - I've only seen castors on the dob base (I thought these were standard, but I guess they must be diy mods). I just Googled "equitorial platform" - loads of DIY info, webring, youtube vids. I must investigate later (one of the hazards of still working for a living).

[david's dob]

as other people have said it is do-able, unfortunately with webcam imaging there is a lack of exposure (the amount of light the scope gathers) so longer the exposure more light is collected to get the super images that you see for deep sky objects, not impossible, but you can get deep sky objects for example andromeda galaxy pretty visable to the naked eye in dark skies, so on a webcam image you would most probly see the bright core, or the Orion Nebula.

i myself have just started webcam imaging and looking to get easy DSO's like the double cluster and see what i can come out with.

[valleyman]

I did some pics with my dob the other day and at best without nudging you get about 15 secs and thats a big target, with the planets you will get much less time.

and using a barlow you can half that time

[russ]

I started out imaging through a dob (Orion XT10) and it was very very challenging and mighty frustrating. But was possible. But with a barlowed image you are talking about just a few seconds on screen.

Visual with the dob, even upto 300x, i find a doddle. Nudging becomes second nature and i no longer know i'm doing it. Just natural.

You do have the option to EQ mount the 200P tube on something like an EQ5 or HEQ5. I mounted mine on a cheap EQ5 and with a motorised focus, it was perfectly acceptable for planetary imaging.

[themos]

At 200x with a Plossl eyepiece, your field of view is a quarter of a degree (52 degrees divided by 200) or 15 arcminutes. The equatorial stars go past at 15 arc-minutes per minute, so you'd get about 60 seconds from edge-to-edge, worst case.

Webcam: with a Barlow to push the focal ratio to f/30, say, and an 8" aperture, that gives you an effective focal length of 240" compared with a sensor size of about 1/4". That's about a milliradian angle, or about 3 arc-minutes (one fifth of the angle we had in the visual example). So the time to transit the chip would be about 12 seconds. I record frames a5 fps (to avoid compression in the webcam at hogher rates) so I would get maybe 60 frames, not good. Some tracking is needed.

Luckily, planets are best imaged when they are in the South (and as high up as they are going to get that night). In the South, tracking is easy, just push the scope in azimuth. So, even a rudimentary azimuth tracking contraption would yield benefits.