太陽派對 - 補課篇 (20110314)

[Robin]

Full disk pics

请问David老师，这几张太阳全身照用的是什么镜子和相机？我有听过LS60的使用者说用了BF1800的遮挡滤镜会出现不平均照明的情况，所以他考虑上BF3400，我听了很疑惑。

[David]

Full disk pics

请问David老师，这几张太阳全身照用的是什么镜子和相机？我有听过LS60的使用者说用了BF1800的遮挡滤镜会出现不平均照明的情况，所以他考虑上BF3400，我听了很疑惑。

APM 80mm refractor (f=480mm) and DMK41 camera were used. I doubt that the problem can be solved by BF3400. In general, I find that the more pictures you stitch together to make a full disk, the more serious the non-uniform problem will affect your processing. So I usually try to avoid making mosaic. Therefore I use a camera with big CCD DMK41 and a telescope with smaller focal length.

[Robin]

Full disk pics

请问David老师，这几张太阳全身照用的是什么镜子和相机？我有听过LS60的使用者说用了BF1800的遮挡滤镜会出现不平均照明的情况，所以他考虑上BF3400，我听了很疑惑。

APM 80mm refractor (f=480mm) and DMK41 camera were used. I doubt that the problem can be solved by BF3400. In general, I find that the more pictures you stitch together to make a full disk, the more serious the non-uniform problem will affect your processing. So I usually try to avoid making mosaic. Therefore I use a camera with big CCD DMK41 and a telescope with smaller focal length.

This is a solar disk imaged with a LS60DS with B1800 and SkyNyx 2-2M (1/1.8" chip). I am sorry as my skills aren't that good but I can't really see any significant flaw especially in terms of illumination. May I know your opinion?

[David]

This is a solar disk imaged with a LS60DS with B1800 and SkyNyx 2-2M (1/1.8" chip). I am sorry as my skills aren't that good but I can't really see any significant flaw especially in terms of illumination. May I know your opinion?

I think it is a very nice picture. I assume that the vertical 'crack' on the right comes from stacking. I usually use the 'blur' function in Photoshop to remove it, or you can try to stack with avistack2. A 'flaw' is that the brightest part of the sun is off-centre. The top part is darker than the lower part. But I have this problem with my setup too sometimes.

Is it a one-shot pic or mosaic? You use a large CCD and so I guess it is at most a 2-frame mosaic. I had done a 2-frame mosaic with LS60TDS50 before. The non-uniform illumination was not obvious:
viewtopic.php?f=19&t=62

However, if you stitch 4 frames or more together, the problem may become much worse. We had a gathering a few days ago and we had a demonstration on how to eliminate the non-uniform brightness in mosaic. So it is a problem that we face a lot. However, in our cases, we don't have a big blocking filter like B1800.
viewtopic.php?f=15&t=1175

One thing you may try is to shoot a 4-frame mosaic with a barlow. See if the problem becomes more obvious. But may be it is best to be happy with your setup rather than digging problems out of something you are already happy with!

[Robin]

This is a solar disk imaged with a LS60DS with B1800 and SkyNyx 2-2M (1/1.8" chip). I am sorry as my skills aren't that good but I can't really see any significant flaw especially in terms of illumination. May I know your opinion?

I think it is a very nice picture. I assume that the vertical 'crack' on the right comes from stacking. I usually use the 'blur' function in Photoshop to remove it, or you can try to stack with avistack2. A 'flaw' is that the brightest part of the sun is off-centre. The top part is darker than the lower part. But I have this problem with my setup too sometimes.

Is it a one-shot pic or mosaic? You use a large CCD and so I guess it is at most a 2-frame mosaic. I had done a 2-frame mosaic with LS60TDS50 before. The non-uniform illumination was not obvious:
viewtopic.php?f=19&t=62

However, if you stitch 4 frames or more together, the problem may become much worse. We had a gathering a few days ago and we had a demonstration on how to eliminate the non-uniform brightness in mosaic. So it is a problem that we face a lot. However, in our cases, we don't have a big blocking filter like B1800.
viewtopic.php?f=15&t=1175

One thing you may try is to shoot a 4-frame mosaic with a barlow. See if the problem becomes more obvious. But may be it is best to be happy with your setup rather than digging problems out of something you are already happy with!

I am not sure how many pieces were there in the mosaic but I am quite sure that it's definitely a mosaic.

The images taken with your LS60TDS50 are seriously impressive. The uneven illumination is almost non-existence. This is my friend's setup and he is thinking that the culprit is the blocking filter which I strongly doubt so as he already uses a BF1800. I am quite a casual person, till now, I am still quite satisfied with my corrector plate broken LX90.

http://www.astronomynotes.net/2009/04/1 ... %e4%ba%86/
http://www.astronomynotes.net/2009/04/1 ... cked-lx90/

By the way, following is the reply I received from Andy Lunt regarding the uneven illumination occurred in my friends' LS60DS.

Due to the need for tilted optics in the system to offset ghosting and back reflections, uneven illumination can happen.

Have the friend rotate the front DS filter slighly (<180 degrees) with respect to the LS60T in order to even out the field. The illumination will move alround as the filter is rotated.
Careful tilting of the filters is also needed. People have a tendancy to over tilt which causes a "sweet" spot in the field. While this sweet spot my have the appearance of a narrower bandpass, it is done so at the expense of the the rest of the field.

It is a bit of a technique to get the ghosts out, the bandpass leveled, and the field illuminated.

The B1800 is certainly large enough. the issues are not the result of the BF.

[universe24]

Robin, why you so sure that it is a mosaic? It seem that the "cracks" is from stacking...
Do you know the telescope focal length of your friend setup?
Try what Andy Lunt suggested. It do help. The issues really should not from the BF.