2:16 you actually _have_ to take filters into account, because while they do not alter the direction of the light going in and out, they _do_ affect the focal distance a little bit, as the light refracts and takes slightly different path while through them. As a result they will "push" the focal distance ever-so-slightly outwards, and the amount of distance pushed will depend on the thickness of the filter's substrate and its refractive index. In most cases the effect is very slight, but when using fast optics with short focal distances, this effect can become noticeable. Which is why when shooting with filters you will want a separate Luminance filter that is just a piece of clear substrate, and why you should have filters of the same series, to maintain _parfocality_ between them.
Love the look of the channel and the videos. It all looks very professional and you clearly know your stuff. Have you thought about doing interviews with other well known space experts in the field? I would love to hear you in conversation with other astronomers, scientists and even astronauts!
@cosmic_curiosity I think that would be awesome and good for the channel. It looks really slick, you've done a great job actually. You deserve to do well from it.
What about the use of thin-spacer rings for camera orientation adjustment such as with your filter wheel.... The spacer ring would be placed between the camera and filter wheel back-side... I assume it still counts towards backfocus since you often adding 0.3mm, 0.8mm, 1mm ... I ran into this issue using my ASI533 and EFW to orient my camera strait with the EFW.
Backfocus ONLY applies when a flattener/coma corrector is used and is the distance where the flat plane is projected. If you don't use a flattener / coma corrector there is no such thing as back focus. As such it's a bit of a misnomer - it would be clearer if it was called "flat plane distance"
Did you know my book "The Cosmic Field Guide" is now avilable at deepspacebooks.com/shop/p/cosmic-field-guide-first-edition
2:16 you actually _have_ to take filters into account, because while they do not alter the direction of the light going in and out, they _do_ affect the focal distance a little bit, as the light refracts and takes slightly different path while through them. As a result they will "push" the focal distance ever-so-slightly outwards, and the amount of distance pushed will depend on the thickness of the filter's substrate and its refractive index.
In most cases the effect is very slight, but when using fast optics with short focal distances, this effect can become noticeable.
Which is why when shooting with filters you will want a separate Luminance filter that is just a piece of clear substrate, and why you should have filters of the same series, to maintain _parfocality_ between them.
Interesting. Thanks for the Explanation!
Love the look of the channel and the videos. It all looks very professional and you clearly know your stuff. Have you thought about doing interviews with other well known space experts in the field? I would love to hear you in conversation with other astronomers, scientists and even astronauts!
That is absolutely something i want to do yeah
@cosmic_curiosity I think that would be awesome and good for the channel. It looks really slick, you've done a great job actually. You deserve to do well from it.
What about the use of thin-spacer rings for camera orientation adjustment such as with your filter wheel.... The spacer ring would be placed between the camera and filter wheel back-side... I assume it still counts towards backfocus since you often adding 0.3mm, 0.8mm, 1mm ... I ran into this issue using my ASI533 and EFW to orient my camera strait with the EFW.
Yeah that would count too. Everything that changes the distance between the camera and the telescope counts.
Backfocus ONLY applies when a flattener/coma corrector is used and is the distance where the flat plane is projected.
If you don't use a flattener / coma corrector there is no such thing as back focus.
As such it's a bit of a misnomer - it would be clearer if it was called "flat plane distance"
Actually it's opuses, if it's too far the stars form concentric trails