Connecting DSLR + Barlow to SCT (cheaply & safely!)

[Xiga]

Hi guys

I've searched all over, but I couldn't find what I was looking for, so I thought i'd post in here. Sorry if this is in the wrong section, but I thought seeing as I am looking to do this for Planetary photography that it would be best in here.

So I have a C8, a Canon 60D, and a cheap Celestron X2 barlow (unthreaded). I am looking to start out in AP and will try and get some images of Jupiter & Saturn this winter, so I have bought & read Jerry Lodriguss' excellent CD-Rom Book 'A Guide to DSLR Planetary Imaging' so i'm almost good to go. I just need some adapters and possibly a new barlow. Oh, and i'm not looking to spend big here, i'm hoping it can all be done for £75 or less, but I can push that a bit if needs be.

So I know I need a T-Ring, these are pretty cheap, I think Amazon do them for about £10-15.

I've also seen the Celestron T-Adapter, they go for about £15.

These 2 alone should be enough for me to connect the camera securely, however, what about introducing a barlow into the imaging train? (essential for planetary). I have seen barlow's that have T threads in the top (for screwing directly into the T-Ring I presume) but then how would one securely connect the bottom of the barlow to the telescope or T-Adapter? Is there another type of adapter I have missed that will do the job for me, and within budget? If there is a way for me to use my existing barlow then great, but if needs be I will buy another. Also, keeping the total length of the imaging train close to optimum will be important (Jerry speaks of using F20 for average seeing and F30 for excellent seeing, but apparently using a camera adds additional magnification so I would need to factor this in as well, I don't want to be closer to F30 most of the time as I will just end up losing detail).

Just need some advice guys before I go and buy the wrong thing(s)!

Cheers all, and clear skies!!!

[jambouk]

Get one of these which will fit i to your barlow (assuming it is a 1.25" barlow) one end, and screw onto your t ring the other:

http://m.ebay.co.uk/itm/161217816379?nav=SEARCH

And one of these t rings for your canon:

http://m.ebay.co.uk/itm/121211245852?nav=SEARCH

If you hunt around you can get them both as one package.

James

[jambouk]

Regarding F/20 - f/30, the camera itself doesn't add any magnification as there are no optics in it when used at "prime focus". What you'll find is that the native focal length of the scope will be roughly doubled by a 2x barlow, and dividing that nee focal length by the aperture will give you the new f/ value, which will be 20ish. To be precise, you'd need to know the actual focal length, and this will vary as you add adapters and the like at the back of the scope, and as the primary mirror moves inside the scope to achieve focus, but i wouldn't worry about that.

So i think your set up with a 2x barlow would give you about f/20.

Going back to the magnification topic, the longer the focal length, the more narrow the field of view which is spread out over the same area of the chip in the camera. So it gives the impression that a longer focal length gives more magnification, but people get heated about what is and isn't magnification, so now i just think of this as projection, and longer focal lengths result in projecting smaller bits of the sky which makes the subject appear bigger...

James

[jambouk]

Finally, and before everyone else jumps in, why not use your £75 to buy an astro webcam?

A webcam using usb2 will be able to achieve high frame rates, and not result in any compression of the data, and therefore potentially better planetary images.

There are some impressive dslr planetary images out there, but i suspect if you used the same scopes on the same nights and processed the same, and compared the results of a dslr vs a webcam in a blind test, i think the judges would favour the webcam images.

Down side is that you'd need a laptop to capture the data rather than the stand alone dslr.

Just a thought.

Good luck with it all!

James

[jambouk]

Oh, and keep an eye on the jet stream, if it is over head, either don't bother trying to capture planetary data else don't be too harsh on yourself when you see the results:

http://www.netweather.tv/index.cgi?action=jetstream;sess=

And focus is really tricky but worth taking your time with.

Don't expect the get good results from every imaging run you do; if you have a jet stream-free night and no cloud, capture lots of runs, 10, 20, and process them all another day.

James

[PeterCPC]

If you are going to use a Canon DSLR I recommend using Backyard EOS to capture images. I find it so easy to use - APT is free but not, in my opinion, so easy to use. BYE can be used for a month free to see if you like it and the cost after that is quite small.

Peter

[Xiga]

Thanks for the info guys, much appreciated.

James, a dedicated webcam is not an option right now, as is computer control. At the moment all my observing is done at a remote location, so lugging around a laptop will only be possible once i move house to somewhere that actually has a garden! lol

Plus, my Canon60D has a special Movie Crop mode which records the centre 640x480 pixels (at 1:1 pixel ratio) and also at 60fps, from what i've read this should give me good results.

I also should have given a bit more detail on my setup:

I have a HEQ5 Pro so hopefully tracking, even at high levels of mag/projection, should be possible even for a noob like myself

All my accessories, of which there are not many, are 1.25". This includes the standard visual back that came with the scope. I also just have the basic focuser, which might prove troublesome when i get to focusing, but that's a problem for another day.

I don't plan on using the diagonal for the imaging

In terms of the adapters though, forgive me but i'm still a bit confused. In the 2 items linked above, i can see that it goes Camera->T-Ring->T-mount. I think the T-Mount is threaded at the bottom, so if i bought another barlow, such as this one from FLO:

http://www.firstlightoptics.com/skywatcher-eyepieces/skywatcher-deluxe-2x-barlow.html

then it would screw directly into the end of the T-Mount.

But now what? I don't want to trust my heavy DSLR (which is also the family camera) to a couple of thumbscrews, each connection point really needs to be screwed in securely, so how do i go from the barlow (which i don't think will be threaded at the bottom) to the the scope?

[jambouk]

How do you normally attach the barlow to the scope? That will be the usual way. If it is two thumb screws, then that will be the way. It is the way most of us do it. You need to see if that feels safe. If not, then think about using the diagonal and then the weight of the camera will be pushing down, rather than pulling out.

The nose piece slots inside the barlow, it doesn't screw onto it.

You'll need to check, but even at 640x480 i think your camera will compress the video and you will have less data than if using a webcam. Many people take laptops to the field. If the laptop battery is n't good enough to last an hour, you can get a charger off ebay to run it off the battery you are using to power the mount, or from the car 12v lighter socket.

James

[jambouk]

I think there is an adapter which goes from sct visual back to 1.25" compression ring/click lock, which the barlow would slot into, and the compression rung would tighten around it, but still not an actual screw fit.

You could ask FLO if there is a screw mechanism, but i don't think it is necessary.

James

[Xiga]

Thanks James. I know a dedicated webcam will more than likely give better results, but given I have to do all my stargazing at a remote location and am already lugging a fair bit of kit with me, not having to ad a computer into the mix is a big plus for me right now, not to mention the additional savings! It's true the camera will only produce 8 bit videos, but apparently some very decent results are possible, more so than with the regular video modes of most DSLRs. Plus, I may try installing Magic Lantern at some point, which should open up the possibility of shooting in 14 bit.

So I've done some more searching this evening, and this is where I'm currently at:

T-Ring

http://www.amazon.co.uk/Celestron-T-Ring-Adapter-Digital-Cameras/dp/B000237C9M/ref=sr_1_1?ie=UTF8&qid=1415750428&sr=8-1&keywords=Canon+eos+t+ring

Or

http://www.amazon.co.uk/Canon-EOS-T-Ring-Revelation/dp/B0039ZHWYK/ref=sr_1_3?ie=UTF8&qid=1415750428&sr=8-3&keywords=Canon+eos+t+ring

Not sure if it makes a difference which I go for.

Adapter to securely fix a Barlow to the back of the scope:

http://www.firstlightoptics.com/adaptors/baader-clicklock-2-125-adapter-2956214.html

This will take the place of the standard 1.25" visual back I'm currently using. I know I could just use the 2 thumbscrews on my current visual back, but I don't want to trust the weight of the camera just to those!

A Barlow with T threads to connect between the Baader adapter and the T-Ring on the camera:

http://www.teleskop-express.de/shop/product_info.php/info/p7095_TS-Optics-2x-Barlow-1-25---with-integrated-T-thread-and-Photo-Adapter.html

This one sounds promising as it sounds like it will do x2 and x2.5, it has the T threads, and they also sell them through Amazon.

Total price is a little over £100.

Any thoughts guys? Will these parts work as expected?

Thanks in advance for your input as always!

Ciaran.

[jambouk]

How does the baader adapter attach to the back of the scope?

Planetary imaging is much more tolerant of light pollution than imaging DSOs so can often be done from urban locations, like my own. If you don't already own a laptop i appreciate the expense issue, but if you do own one, i'd seek a wider range of opinions about dslr vs webcam planetary imaging before spending your valuable cash. Yes there are some nice results from dslr, but in a my non-scientific comparison way i think the webcam ones are a step above. I have no vested interests, i just want you to be 100% sure before you splash the cash

Where in the world are you?

James

[Xiga]

From the look of it, i think the Baader adapter just screws directly onto the back of the scope, just as you would do with a visual back? If anyone has any experience with one of these i'd be grateful to hear some feedback.

I live in a flat in Belfast, Northern Ireland. Which means i don't have a garden to make use of, even for bright objects like the planets. So every session means loading up the car for a 45 minute drive each way. Plus there is the ever-present rubbish weather to deal with as well! lol

At some point much further down the line  i will probably look into guiding and using a laptop etc, but for now i think i will be happy experimenting with the Canon (im still very much a novice tbh, i've only had my telescope a couple of years).

[jambouk]

Ok. I'll drop the webcam nagging

That adapter to me looks like it just has a 2" nose piece, and is threaded to take 2" filters. I don't think that will screw onto an SCT visual back.

I'd email FLO, and say you want something like this but which screws onto an SCT visual back; they are very good at replying.

James

[jambouk]

I think you might need this:

http://www.firstlightoptics.com/adaptors/baader-click-lock-2-for-celestron-meade-sct.html

And then a 2" to 1.25" reducing adapter, but i can't see that will be a screw thread, so will be relying in screws / compression ring holding things together, which is what most of us do, but which you are scared about.

Definitely email FLO and tell them exactly what you are trying to achieve: have only screw threaded connections to attach a 2x barlow (not yet purchased) with a canon dslr onto the back of an SCT.

Do let us know what they say.

James