Tag: m101

M101 AgainAgain

This is over-processed but I kind of like it. This is 60+ exposures through the Takumar 200mm lens at about f/5.6. Each exposure was 60 seconds at ISO 1600. I had only 3 darks and 9 bias shots and no flats. I used SiriL for the processing following this tutorial. After Siril I used Paintshop Pro 5 to boost the contrast quite a bit further further – (Colors/Brightness/contrast=59 with no added brightness).

This is about 25% of the full image. I don’t care too much about anything outside the central image but i do note really bad vignetting on the full shot as shown below. I’m going to take some flats to see if they help.

I also note that my stars are not great – a little stretching top to bottom. I had what i consider excellent alignment – within two arcminutes. I may not have been perfectly level but i was close.

Repeating Galaxy Hunting M101

This is not awful at all! Nine out of 14 exposures 90 seconds, ISO 800, f/5.6 with the Takumar 200mm lens on the canon t3i. The spiral of the pinwheel nebula is faint but clear. and you can see the faint fuzzy of NGC 5474 below and to the right. In fact, aided by Astrometry.net and the eye of faith I can see at least NGC 5473 below M101 and left, NGC 5485 still lower and left and NGC 5422 above and left of M101.

I used DeepSky Stacker per this tutorial which is clear and specific. I had taken more images earlier in the month and stacked them then with less success.

More Stars, No Smudge

DSCN1694_Max_crop
I tried last night 4 second exposures at ISO 400, 300mm focal length and f/5. I took 10 shots tried a few ways of stacking them including deepskystacker, rotn’n’stack, layers in paint shop pro, and a home-brew python/opencv program that just added the pixel values. The best result I got was rot’n’stack. Four seconds is clearly pushing it, the stars show definite trailing but it’s not awful. I certainly see stars that didn’t show up in the ISO 6400 1/2 second images. The two below the red circle where the pinwheel should be are magnitude 8 and 9!
Unfortunately, the 4 seconds at ISO 400 is sort of a sweet-spot. The slowest speed at ISO 800 is 2 seconds which would be the same. I can try ISO 6400 1/2 second which is nominally better but that’s what i had tried the other night.

With the Canon the longest focal length is 85mm equivalent so I could go to say 15 seconds for equivalent trailing and i could use ISO 800 or more but at 80mm focal length equivalent the smudge would be pretty small and at f/5.6 the light gathering is lessened. I may try it on the next clear night along with 1/2 sec ISO 6400 on the nikon. Playing around with telescopius I think that, at 85mm on the canon, M101 would cover about 1% of the sensor which would translate to a bunch of pixels.

Also from telescopius I get the following charts for pinwheel which shows surface brightness as 23.8 mag/arcsecond. I think that’s very dim. Andromeda at 22.2 is just a bit better. Bode’s galaxy at 21.7 a bit better still.

Somebody on reddit just told me i’d need to stack hundreds of exposures to see it – that’s not going to happen!