Jupiter and Europa

[oldfruit]

Managed to capture Europa just before it was about to dissapear behind Jupiter tonight. Seeing was no great, but with clear skies and no Moon who am i to moan .

Thanks for looking.

Mark.

[Hypernova]

Nice

Was that with the Helios 200 and the SPC900? What f/ratio was this taken at?

[Clayton]

Nice one Mark

[oldfruit]

Nice

Was that with the Helios 200 and the SPC900? What f/ratio was this taken at?

Yes this was taken with the same kit. Not sure of the exact f/ratio as i was using a tv 3x barlow and 2 empty barlow tubes as extensions.

Thanks for the comments.

Mark.

[Clayton]

Looks like around f24.2 Mark (based on a pixel size of 5.6 microns not certain that it is the correct size??)

[oldfruit]

Looks like around f24.2 Mark (based on a pixel size of 5.6 microns not certain that it is the correct size??)

How on earth do you work that out??

[Clayton]

There is a formula floating about, as below;)

Something that comes up frequently in planetary imaging is the question of determining the effective focal length of the telescope. This is a non trivial exercise as there is normally at least one barlow element in the optical train, and the actual amount of magnification provided will depend on the specific optical setup - most barlows will either increase or decrease from their nominal power as the camera is moved closer or further away from the top optical element.

For example, the TeleVue 5x powermate will increase its power by 1x for every 35mm of extra distance introduced between the top of the powermate barrel and the focal plane of the camera. (reference: Televue Powermates).

In practice, this and other variables in the optical system make it very difficult to accurately calculate the effective focal length of the instrument.

The solution is to work backwards from a captured image and calculate the focal length directly. All you need to know the pixel size of your camera (in microns) and then use the following formula:

F = 206.265 x P x U

---------------

O

P is the size of the object in pixels as captured

U is the pixel size of the camera in microns

O is the true size of the object in arc-seconds

F will be the focal length as calculated from this formula, in mm

After that you simply divide the Focal Length by the Objective size in mm

[oldfruit]

Thanks Clayton for explaining that.

[chris285]

much better than i could see with my borrowed Celestron XLT 150 last night north of Lincoln, nice image

[rickygoespop]

just a quick one but what is the difference between having clear skys and not good seeing? im all new to this but i would say clear skys means good seeing but obviously i need more info ....cheers..rich

[oldfruit]

just a quick one but what is the difference between having clear skys and not good seeing? im all new to this but i would say clear skys means good seeing but obviously i need more info ....cheers..rich

Sometimes the sky can look crystal clear but if the atmosphere is turbulent then it will cause bad seeing. Sometimes it can be so bad that it can be almost like looking at something through running water where the image appears distorted.

[smerral]

Great image - sharper than what I managed through the Mak here in Caithness. I've seen several really fine images from last night taken further south where the seeing appears to have been rock solid. That's one of the better ones though.