Questions on DSLR for astrophotography

fizzy123 · Post by **fizzy123** » Sun Sep 12, 2010 9:22 pm

Hi folks, just want to find out some information with regards to Panasonic Lumix DGC-10K DSLR for astrophotography.

How does one convert mm to X? Say I have a camera that has optical zoom of 3X, how many mm does this equate to?

My Micro 4/3 DSLR claims that the lens is 14-42mm in focal length, but on the webpage, they also wrote 28-84mm in 35mm format. What does the 35mm format means?

Comparing a real DSLR and a pretender DSLR, like a micro 4/3 device, what are the forseen problems one might encounter with using a micro 4/3?

Lastly, I am planning to buy a T-adapter for this camera I described above. The price quoted by Sim lim is 240 while AMK photography shop quote 260. I would like to know if this is an accurate and honest quotation of the adapter? From what I know, most T-adapters real DSLR are under 100, so is the price of 240 normal for micro 4/3 DSLR?

Zephyrus · Post by **Zephyrus** » Sun Sep 12, 2010 10:33 pm

Hehe, I don't know much about about the micro 4/3rd system but I do know that those prices are hellish. I remember purchasing a cheap t-2 mount adapter for my Canon 50D from eBay, then bought a t-adapter separately.

I recalled the T2 mount to EOS being less than US$10. I can still find it here: http://cgi.ebay.com.sg/T2-T-mount-Lens- ... 4cec7f9290 (The same eBay store I bought from)

I can't remember where I bought the t-adapter to screw in to the mount though, but it was under US$50. So yeah, the cost is between S$80 to S$100.

As for the differences, well the "pretender" DSLR is actually very capable as it can do everything the DSLR does including filters and everything (except ergonomics sucks), at a lower cost because the sensor is smaller hence lens can be smaller and cheaper also. But like I said, sensor size is smaller. I'm not an astrophotographer so I don't know, but I believe sensor size is important during astrophotography and perhaps a more experienced astrophotographer can tell you?

Infact, a DSLR is never really recommended for astrophotography. A dedicated ccd/cmos sensor would be better for all the long exposures because DSLR have more heat issue than those dedicated (and freaking expensive) sensors for astrophotography. Most DSLR that are used for astrophotography are modified to remove the UV/IR filter for spectrum enhancements and probably some fans to cool it.

cloud_cover · Post by **cloud_cover** » Mon Sep 13, 2010 1:21 pm

The micro 4/3 use a sensor that is almost DLSR sized so in terms of noise performance they should be similar to a DX/APS-C sized DSLR, if the make and specs of the sensor are the same, not counting software compensation.
I personally think micro 4/3 are being marketed based on their size advantage as getting an entry level DSLR with kit lens can actually be cheaper. Personally, I feel although the camera is smaller, when combined with the lens, much of the advantage is negated and a conventional DSLR "holds" better in the hand with controls better placed for easy reach.
I agree with Zeph that noise and heat are issues with entry level DSLRs, although that's not to say it can't be overcome with stacking or reducing the ISO. Although there's a lot of literature on modding DSLRs to remove the IR/low pass filter to allow better H-Alpha, an unmodded DSLR can still do as good a job on everything else other han H-Alpha nebulae. Also, a H-Alpha blocker merely means increasing exposure time on a H-Alpha source. Again, having siad that, some D700/D3 users have reported excellent unmod shots on M42. I can't find the unstacked pic where even the dust lanes are visible around orion (unstacked), but here's a link for a D3 shot at 70s, unstacked, at ISO 1600 via an 1000mm/f5 telescope (which makes it an 8" aperture, prob a newt given the f5 rating). Ignore the coma (he needs a paracorr/MPCC) but check out the detail of that H-Alpha nebula

Edit: Oops! Here's the link
http://forums.dpreview.com/forums/read. ... e=26047274

orly_andico · Post by **orly_andico** » Mon Sep 13, 2010 1:25 pm

CC, not true. Micro-4/3 is 1/2 the area of APS-C, which in turn is 1/2 the area of FX / full-frame.

I don't think anybody says that APS-C is "almost FF-sized" :-)

And where's the link?

Back in 2002-3 I was drooling over these shots taken by Johannes Schedler using the (by now ancient) Canon D60 of the Pillars of Creation. But the thing is, Johannes' observatory is in Styria in the Austrian Alps where it's literally below freezing. :-P

ed: Fizzy, 240 for a T-adapter?!?!?! order it on ebay.
http://cgi.ebay.com/T2-T-mount-adapter- ... 366wt_1137

This guy is selling them for $6 USD. That's inclusive of shipping!

You will also need a 2" to T-adapter though.. this one is $30 USD:
http://cgi.ebay.com/2-T-T2-Mount-Prime- ... 1539wt_911

so basically

Telescope focuser (2") ---> 2" to T-adapter ---> T-adapter to 4/3 adapter ---> your camera

If your telescope has only a 1.25" focuser... then you have a problem. Your DSLR will be severely vignetted due to the small diameter of the 1.25" focuser tube.

cloud_cover · Post by **cloud_cover** » Mon Sep 13, 2010 1:32 pm

Eh, I thought I read a pamphlet saying the sensor is near APS-C sized? Hmm..... overly optimistic marketing. Grrr..... I stand corrected again

orly_andico · Post by **orly_andico** » Mon Sep 13, 2010 1:35 pm

here are some DSLR shots..
http://www.astropix.com/HTML/I_ASTROP/NIK_CAN.HTM

also there's that amazing M31 with a Pentax K-x and Pentax 67 lens that I'm drooling over...

orly_andico · Post by **orly_andico** » Mon Sep 13, 2010 1:45 pm

Here's an article on 4/3
http://www.cambridgeincolour.com/tutori ... r-size.htm

It certainly "looks" like APS-C is not much smaller than FX, right? and 4/3 is not much smaller than APS-C.

The thing that is confusing is that, if you overlay an APS-C on FX, they "look" similar, but if you turn the APS-C (18mm x 24mm) sensor by 90 degrees, you will see that its longer dimension (24mm) is exactly the same as the shorter dimension of FX! (which is 24mm x 36mm)

Which shows that APS-C is 1/2 the area of FX.

Meanwhile 4/3 sensor is 1/2 in both dimensions of FX, e.g. it is 12mm x 18mm (1/4 the area of FX) and therefore it is 1/2 the area of APS-C.

Personally for small camera, the Sony NEX3/NEX5 is probably the nicest. APS-C sensor in a body that's smaller than the Micro-4/3 bodies. But I digress.....

andeelym · Post by **andeelym** » Mon Sep 13, 2010 4:04 pm

Recently I bought this (http://cncsupplyinc.com/true2_eos.htm) for my Canon DSLR (5D Mark II). I previously used a 1.25" system and suffered from heavy vignetting. So I go for a one-piece 2" system for the biggest available aperture.

orly_andico · Post by **orly_andico** » Mon Sep 13, 2010 4:14 pm

trouble is when using Maks or SCTs.. most of them have 1.25" focusers unless you buy a 2" visual back or Petersen Eye Opener....