12 replies to this topic

[otocycle]

The Astronomik Ha 12nm CCD clip filter has given new life to the old M42 lenses I have lying around.    I wanted to see how the 300mm f/4 Pentax Super-Takumar would perform in Ha and it looks promising.   Disregarding the noise, I jacked the unmodified Canon T6i's ISO to speed things up, and the North America Nebula / Pelican just jumped right out.

 

This is about 37 minutes total with 5 darks.   Piggyback on AG8/Orion Atlas EQ-G with PHD2 guiding.

 

Nice break from planet season !

 

 

Edited by otocycle, 12 July 2018 - 05:37 AM.

[aneeg]

Very nice, indeed. Makes me want to try my old Takumars of 200, 400 and 500mm lenses.

 

Arne

[SandyHouTex]

The Astronomik Ha 12nm CCD clip filter has given new life to the old M42 lenses I have lying around.    I wanted to see how the 300mm f/4 Pentax Super-Takumar would perform in Ha and it looks promising.   Disregarding the noise, I jacked the unmodified Canon T6i's ISO to speed things up, and the North America Nebula / Pelican just jumped right out.

 

This is about 37 minutes total with 5 darks.   Piggyback on AG8/Orion Atlas EQ-G with PHD2 guiding.

 

Nice break from planet season !

 

 

NGC_7000_300MM_T6I_Ha.jpg

Good to know.  I purchased the same lens awhile back and haven't had a chance to use it.  Great pic.

[otocycle]

Very nice, indeed. Makes me want to try my old Takumars of 200, 400 and 500mm lenses.

 

 

Thanks....I also have the 200mm f/4 Super Takumar....still looking for that big 500mm ebay bargain.    These prime lenses focus a little bit shorter in Ha, but stay pretty good right to the edge of the APS sized sensor.

[SandyHouTex]

Thanks....I also have the 200mm f/4 Super Takumar....still looking for that big 500mm ebay bargain.    These prime lenses focus a little bit shorter in Ha, but stay pretty good right to the edge of the APS sized sensor.

The 500mm would be great, but they’re expensive.

[aneeg]

I found mine on eBay and paid $180!

 

Arne

[Alone_Ghost]

not bad!

[Kendahl]

I'm going to the Nebraska Star Party next month and hope to capture this and the Veil Nebula.

 

What were your ISO and subexposure duration? Did you have the lens all the way open to f/4?

 

My camera is an unmodified Canon T3i. Will it capture these nebulae as is or do I need a filter or a modified camera?

 

I see you used an Ha filter attached directly to the camera sensor. My wife has a 2" Astronomik UHC filter which I could borrow and screw into my 2" camera adapter (https://agenaastro.c...-canon-eos.html). Will that work?

[otocycle]

 

....What were your ISO and subexposure duration? Did you have the lens all the way open to f/4?

 

My camera is an unmodified Canon T3i. Will it capture these nebulae as is or do I need a filter or a modified camera?

 

 

 

The subs were taken with an unmodified Canon T6i with Astronomik 12nm Ha EOS clip filter and Pentax 300mm Super Takumar prime lens wide open at f/4.

 

Ignoring the expected noise, subs were:

 

• 1x60sec @ ISO 12800
• 1x180 sec @ ISO 12800
• 5x180 sec @ ISO 6400
• 2x240 sec@ ISO 3200
• 3x180 sec@ ISO 1600
• 5x180 sec @ ISO 6400 - Darks

 

A UHC filter has a much wider band pass than the Ha narrow band, but it will help with light pollution and contrast.

 

Your unmodified T3i can capture this kind of nebula, just not as efficiently as a modified camera.   Just get as much integration time (exposures) as you can....the NGC 7000 region is relatively dim.

 

If you are at a dark site, you will get good results even without a filter.

Edited by otocycle, 18 July 2018 - 02:06 AM.

[Kendahl]

Thanks for the information.

 

My lens is a Canon 100-300 L series f/5.6 zoom. It's not as good as your Takumar nor as fast. However, it's what I have. I think it should be adequate.

 

I was figuring on four hours total exposure for each target beginning a couple of hours after sunset.

 

NSP is a Bortle 1 site. LightPollutionMap.info claims it's 22.00 mag/arc-sec².

[otocycle]

Your Canon zoom should be fine...just be careful with the sub-exposure length if you are not using a narrow band filter.   Brighter stars will tend to flare/bloat more with long exposures, so try various length exposures and see what you get.

 

Here is an example of NGC 7000 North America Nebula with the 300mm Super Takumar @ f/4 with no filters [60x60 sec @ ISO 1600]...under Bortle Scale 5 skies.    I had to keep the subs at 60 seconds because the stars would begin to bloat from the achromatic lens design (compare bright star sizes to those in Ha image above).

 

If you are more experienced at image processing, some of the bloat can be reduced in post.

 

 

Edited by otocycle, 18 July 2018 - 09:47 AM.

[Kendahl]

Brighter stars will tend to flare/bloat more with long exposures

Is it the subexposure duration that bloats stars or is it the product of ISO and duration (i.e. 300 secs at ISO 800 = 600 secs at ISO 400)? I use ISO 800 or 400 to maximize dynamic range and control the histogram by varying duration.

 

Star bloat is a matter of taste. Here is a photo I made of M109 (top right) and NGC 3953 (bottom left) under a Bortle 4 sky. It's cropped to 1.5° x 1.0°. Subexposures were 8 x 480 secs at ISO 800 and f/7.7. I chose to include Phecda in the picture even though it's grossly overexposed.

 

[otocycle]

Is it the subexposure duration that bloats stars or is it the product of ISO and duration (i.e. 300 secs at ISO 800 = 600 secs at ISO 400)? I use ISO 800 or 400 to maximize dynamic range and control the histogram by varying duration.

 

 

Star bloat comes from several factors....exposure duration, chromatic aberration, dynamic range (ISO), focus differences (visible vs. IR light), etc.   Lower ISO  will certainly help. 

 

Stacking images does not increase star bloat in my experience using Deep Sky Stacker.