Bahtinov blunder, accidental genius or serendipity?
Last night (Sat) the seeing conditions were amongst the best I have experienced for a while and after slewing to a bright star to focus the rig, I slewed to the nearby Moon and began a series of 2000 frame captures.
It wasn’t until I worked my way up to the edge of the Moon and saw the blurry limb that the penny dropped; I still had the Bahtinov Mask on the ‘scope - doh. By then, it was too late as the seeing dropped off to just good from excellent.
If you look carefully at the specular highlights, such as mountain peaks or crater rims that catch the light, you can see the unmistakeable Bahtinov mask diffraction patterns…
Once I realised what I had done, I saw the funny side to it but by then, the seeing had dropped off with a change in wind direction and warmer air blowing in.
I decided to process the 2000 frame AVI’s none the less and was astonished at the seeming lack of degradation. I then remembered the topic of “Apodizing Masks” as used by double star observers and a Google search turned up the following useful sites.
So, it seems I got lucky and the Bahtinov Mask somehow supressed the detrimental effects of the low frequency seeing by diffusing the incoming signal?
When I look at thumbnails of the 1024 pixel JPGs in Lightroom, they seem hazy but when viewed at full size, the detail still comes through. All these images have been re-sampled from the full res originals of 1920x1200.
Ok so I can see the overall striation effect, presumably caused by the BMask but through that the resolution certainly "looks" amazing ...so is this an optical illusion or is the spacial resolution really top notch?
Excuse my ignorance but I am not a planetary master
These are some great images. I love the detail, mountains and shadows, rivers etc. Since starting in astronomy 12 months ago I have become obsessed with the moon (I never get bored looking at it and identifying areas). I love the detail that these pics have. What equipment/exposure settings/process was used here. I am slowly getting the gear together to start on some imaging.
Ok so I can see the overall striation effect, presumably caused by the BMask but through that the resolution certainly "looks" amazing ...so is this an optical illusion or is the spacial resolution really top notch?
Excuse my ignorance but I am not a planetary master
Mike
Hi Mike
I’m not sure about what is going on here, but from what I understand, a bone fide "apodizing mask" dumps energy from the central diffraction spike and disperses it into the surrounding diffraction rings. From the links I visited, double star observers use this technique to split difficult doubles, especially where the companions have a large magnitude differential.
There are some thoughts that this technique should not work on obstructed optics such as the Mewlon, as the central obstruction itself lessens the intensity of the central diffraction spike.
It may be that the larger brightness range of the lunar features were levelled a little by the accidental inclusion of the Bahtinov Mask and coupled with the above average seeing, produced some pleasing results. Maybe the real signal was reinforced and the random noise was diminished as a result of the mask?
I’ll have to wait for the optics heavy weights to wade in, as my knowledge on this topic is quite basic.
These are some great images. I love the detail, mountains and shadows, rivers etc. Since starting in astronomy 12 months ago I have become obsessed with the moon (I never get bored looking at it and identifying areas). I love the detail that these pics have. What equipment/exposure settings/process was used here. I am slowly getting the gear together to start on some imaging.
Andrew.
Thanks Andrew and Kim, the Moon is an amazing place to explore through a telescope. I used a Takahashi Mewlon 180 F12, a Televue x2 Powermate and a ZWO ASI174M CMOS camera.
The ASI174M records a “movie file” (AVI) and in this case, I recorded 2000 Frames. I used the application “FireCapture v2.4” to control the camera and save the AVI.
I then used “AutoStakkert!2” to open the AVI and the program then aligns and stacks all the frames together, based on user inpout such as say, only select the top 25% of frames (best image quality) or just the top 300 frames. This means that you can select the frames that were recorded when the seeing was at its best and discard those where the image was mushy or fuzzy due to atmospheric turbulence.
This process improves the signal to noise ratio. That is, the real data which is present on every frame is reinforced whereas the random noise is averaged out.
The camera settings were: Exposure 13.5 milliseconds, Gain=230 with a Gamma=50.
Thank you for that, I will one day head down this way. I am currently putting together an imaging set up and hope to start on it next year. But I am starting with much simpler and basic gear at this stage.
Hello,
I have just come across this thread after a search for apodizing filters. I am really unsure what to make of these images, the detail is amazing yet there is an obvious image defect when viewed from the thumbnails or afar.
Do you think that the defects could be removed with a flat or by dithering?
Those are interesting results Dennis, mistakes get made all the time in the dark, forgetting to remove dew caps etc.
Bigger scopes have smaller airy discs anyway but with your size of scope you may need to experiment on close doubles with/without mask to be certain you are getting some advantage - Antares has a 5th mag blue companion 2.7 arc sec apart and would be very difficult to get a clean split in your scope (I can just manage it with 14" aperture - good collimation essential).
The effect seems to reduce highlights by spreading them out more. I think the excellent detail was down to the seeing on Saturday night not the mask possibly?
After rotating the images 10 degrees CW I used ImagesPlus Local-Line Enhancement and Suppression which reduced vertical lines really well with horizontal width of 5 vert 37.
Those are interesting results Dennis, mistakes get made all the time in the dark, forgetting to remove dew caps etc.
Bigger scopes have smaller airy discs anyway but with your size of scope you may need to experiment on close doubles with/without mask to be certain you are getting some advantage - Antares has a 5th mag blue companion 2.7 arc sec apart and would be very difficult to get a clean split in your scope (I can just manage it with 14" aperture - good collimation essential).
The effect seems to reduce highlights by spreading them out more. I think the excellent detail was down to the seeing on Saturday night not the mask possibly?
After rotating the images 10 degrees CW I used ImagesPlus Local-Line Enhancement and Suppression which reduced vertical lines really well with horizontal width of 5 vert 37.
Very interesting post.
John.
Hi John
I’ve split Antares with a Vixen 4” refractor and stacked Barlow’s with a Meade LPI several years ago, under almost perfect conditions.
Here is a split from Sun 15th May 2016 with the ASI224MC and Mewlon 180 with TeleVue x2.0 PowerMate under less favourable conditions. I also managed a cleaner split with the B&W ASI120MM back in 2013 using the Mewlon 180.
Agree with your comment re good seeing for the above "accidental" lunar images.
Cheers
Dennis
EDIT:
Just found the old Vixen 4” results from the early 2000’s. I still have that Vixen.
This is interesting as many have said ! Grouse moonage indeed, it would be of further interest to have a proper recommended screen made apodized mask and whether it would result differently compared to these with the bahtinov striation mask effects ?
Definitely some very fine & sharp details in view here, excellent
This is interesting as many have said ! Grouse moonage indeed, it would be of further interest to have a proper recommended screen made apodized mask and whether it would result differently compared to these with the bahtinov striation mask effects ?
Definitely some very fine & sharp details in view here, excellent
Hi Bob
In terms of planetary imaging, the use of webcams and “lucky imaging” where you stack 1000’s of short exposure frames to capture the better/best moments of good seeing, probably does'nt require the use of an apodising mask?
It's a really interesting effect. It reminds me of those hybrid images that were floating around recently; You know the ones - where it's a picture of Einstein and Marilyn Monroe at the same time depending if you squint or not.
It's fascinating how from far away (or in the thumbnails) something definitely looks blurry, but in the larger picture, everything looks fine. I'm not sure I understand the apodizing masks, but it seems to me that you have essentially got crystal clear high-frequency detail, but blurry low-frequency data.
In terms of planetary imaging, the use of webcams and “lucky imaging” where you stack 1000’s of short exposure frames to capture the better/best moments of good seeing, probably does'nt require the use of an apodising mask?
Dennis,this same effect was noted about six months ago,using the same mask,also on the Moon by another poster,I forget who it was,but I saved the pics on my hard drive somewhere.
...so is this an optical illusion or is the spacial resolution really top notch?
