DSLR Questions

[Robbie]

Hi All,
I have been imaging with ccd cameras for a few years now and Im keen to buy a DSLR and give that a go.
I have turned myself loose in a few camera stores but always seem to walk out confused and empty handed, I was wondering if someone in the know could just quickly describe the advantages / disadvantages of DSLR over CCD and explain the IR mods eg are they crucial for imaging or can good results be acheived without mods and if modded can the camera still be used for terrestrial use.
Lastly can someone suggest a camera and basic accessories required Ive budgeted for 2 grand and would prefer new gear.

I would appreciate any help in this area from someone using DSLR before I run off and blow my budget on things I dont need.

Robbie

[g__day]

At close to the same pricepoint CCDs (which get very expensive quickly - as they aren't a mass market electronics items like DSLRs are) - dedicated to astro photography will likely perform better than DSLRs - because of four factors - pixel well depth (amount of information store on each pixel), Quantum efficiency of the chip, ability to be cooled well below freezing without exposure to humidity fogging the CCD (vastly lowering dark noise) and much more suitable - if any filters (that don't stop the red Hydrogen Aplha emissions many dark sky object exhibit).

DSLR's on the other hand are more versatile - you can fit many lens to them, they auto focus and you can point and shoot. They have many accessories you can get - useful for daytime shooting. DSLRs generally have much larger chips - making them excellent for wide field (broad shots). As they will generally have a very small pixel size - you will need to consider binning shots maybe 2*2 else you will be wasting resolution if your viewing (arc seconds per pixel) is below seeing conditions at your location.

Modded DSLR (either cooling - ughly but quite effective $1,200) or ones with astronomical suitable filters (that allow Hydrogen alpha light through around $850) will make subjects that radiate strongly in Ha look right. By this I mean consider using an unmodded DSLR - say my Caon 400D - on the Tarantula (NGC 2070). My shots look blue / green - as this object emits strongly in both Oxygen III emission - which the camera gets and sees as blue green - but it also emits strongly in Ha (deep red) but this part of the signal is largely filtered out by my standard DSLR IR filter.

Modded DSLR with astronomical fliters can have a custom white balance set to make them suitable for day time / normal use I believe. You need to check whether auto focus and full automatic shooting mode still works normally.

As DSLR's go I think the Canon's have the edge as they have low to no amp noise nowadays, great signal integrity and remote LiveView (on Digic 4 - the current generation) of DSLR to help check your shot is framed well.

I'd look into the Canon 5D, 50D or 450D + power supply (if you're near mains power where you shoot about $95) + either cable bulb or ShoeString astronomy DSUB (camera -> PC via USB port about $80) camera shot duration control and Canon EOS -> 2 inch OTA adapter (around $50). Add filters or change supplied IR filter to an Astronomical one per your inclination.

See what others think too!

Oh also there are colour and mono CCDs. Colour CCDs work like DSLRs - they have a bayer matrix (2*2 grids - Green, Red, Blue, Green - repeated over and over - with pixels treated to only let one frequency of light it - then adjacent cells mathematically interpolate the colour of each pixel from those surrounding it). Pixels under a Bayer mask may be 4 times less sensitive than mono pixels that see only black and white and need RGB filters to capture colour intensity. Note colour focus at different wavelengths - so with a mono CCD you need to refocus (manually or with a very smart, and often temperature sensitive, very expensive focuser that knows which filter you are shooting thru and hence how to minutely alter focus in or out - very accurately).

Also CCDs are generally 16 bit - old DSLRs are 12 bit chips, newer ones use 14 bit electronics. Two extra bits means four times a chip wil have as much data per pixel to record.

Finally DSLRs being simpler, mean image processing is alot simpler to learn and master - there are less data, meaning options and less ways to go wrong.

Camera specific comparison:

http://www.astropix.com/HTML/I_ASTROP/COMPARE.HTM

12 vs 14 bit Canon DSLR comparision for astro shots:

http://www.astrosurf.com/buil/eos40d/test.htm

[Robbie]

Thanks for taking the time to share that information. I managed to at a cost of mere millions walk out of a store with a canon 50d + 55 to 200 zoom lens then got in touch with supplier for t rings adapters and a piggyback bracket. I spent last night playing with it and was a bit daunted by the functions but after a few hours the penny dropped.
I had to order an ac power supply of course none available locally so I will have to suffer with batts for a while until it arrives.
The live shoot software allows full control from laptop, bulb from the laptop is press to open shutter press to close unlike hands on which is press to open release to close. so no remote is required.

I have been browsing the net for astropics with this camera and I must say even the unmodded pics are impressive so I will use it stock standard and just buy filters as my experience increases.

I cant wait to get to work with this camera and look forward to posing first light with it.

Again many thanks for the info

[g__day]

Robbie,

Well done and good luck. Keep your eyes out for auctions too. I got a Canon EOS1000, 35 - 50mm lens, 35 - 235 macro lens!!! + professional flash and carry case for $90

I chucked the camera, sold the small lens for $50, gave the bag and flash to a friend and kept a perfect almost $900 lens for the net price of $40. Sometimes at auctions you'll find real bargins!