I just got a Pegasus Astro Falcon rotator. I love it. Also no real back focus problem on the Askar FRA400. I just got the 294mm Pro, yes it has it's problems and I would have gone for the 2600mm but the extra $$ weren't there at the time, Now that I'm using it I do like it even with the amp glow and the bin1 mode is awesome. I miss the wider field of view from the 2600 though. I consider my rig complete now FRA400 w/.7 reducer (285mm f3.9), AM5, 294mm Pro, 7 filter wheel w/Antlia 36mm 3nm filters, ZWO EAF, Falcon 2 rotator, Giotto and Alto, Pegasus Power Box, Mele Quieter 3. I just got an EdgeHD 9.25 and getting that set up has been... a pain. I love the images though. Clear skies!
I've never used a rotator and use both of the cameras you mention. Logically, not sure why you would need a rotator on a wide field scope. Also, I shoot my calibration frames once per season because my field of view orientation does not change. This gives me a great result. If you had a rotator, you would need to shoot calibration frames each time you used the scope. Way too much work - at least for me.
Great points! I think the decision to purchase was a carryover from my days as a photographer where I was known to suffer from GAS (gear aquisition syndrome). 😉 I like to learn about new things and wanted the experience of using a rotator. That's why I had no hesitation to remove it. Thank you for taking a moment to drop a comment. Much appreciated. 👍
I'm moving the RedCat and the EdgeHD 8 as well. Dropping both off at Starfront on December 29th. I expect it will take them a couple of weeks to put in place on the piers before I can remote intothem. I expect I will learn a lot! 😉
Let's talk calibration. Your light frame, i.e. the one you take under the stars of whatever target you're shooting, contains a number of unwanted things. Sensor noise. Optical defects. Dark current. Calibration removes those unwanted things. The darks remove additive things like dark current / amp glow. The flats remove multiplicative things like light falloff. But here's the thing - those flats are just lights, so they contain the same type of additive issues like dark current and amp glow. Just like you subtract a dark from a light, so too do you subtract a dark from a flat. Wait a second... so then what is this bias and why do people use them to calibrate a flat? Well, a bias is just an extremely short dark, typically taken at the shortest exposure your camera can do. For cameras like the 294 or 2600, that is 32 microseconds. So why do people use a bias in lieu of a dark to calibrate a flat? Simple: it's convenient. Flats (which remember are just lights) are usually pretty short exposures. We're talking a few tenths of a second or less, especially if you're taking sky flats using our own sun as your light source. Because it is so short, there really isn't time for all of those additive things to have any real impact on the data. The only additive thing we really need to remove is the offset, which is precisely what the bias frame represents. Thus, calibrating a flat with a bias is "good enough". In most cases. The sensor in the 294 is quirky. Whereas quite a few other cameras behave in a predictable, easily modeled linear fashion, the 294 doesn't at extremely short exposures. In fact, it's not until you've gotten to exposure times of around 2 to 3 seconds that the camera behaves properly. This means there's plenty of time for those nasty additive elements to play havoc, and thus you must take matching darks to subtract them all out. Now, there are plenty of people who will swear up, down, left and center that they can take short flats and use biases with their 294. Maybe they got a good sample of the sensor. Maybe they're not getting the best calibration they can and deal with it during image processing. Maybe they just don't know. There are hundreds (perhaps even thousands) of pages of debate on the astrophotography fora about using darks or biases to calibrate flats. My stance on the matter is that using matching darks with your flats is the best way to calibrate, regardless of which sensor you're using. Having written that, with my Poseidon-M Pro (same IMX571 sensor in the 2600MM Pro), I use biases to calibrate my flats and don't even bother taking darks for my lights, instead using the same biases to calibrate them. The old adage do as I say, not as I do is certainly apropos :).
I just got a Pegasus Astro Falcon rotator. I love it. Also no real back focus problem on the Askar FRA400. I just got the 294mm Pro, yes it has it's problems and I would have gone for the 2600mm but the extra $$ weren't there at the time, Now that I'm using it I do like it even with the amp glow and the bin1 mode is awesome. I miss the wider field of view from the 2600 though. I consider my rig complete now FRA400 w/.7 reducer (285mm f3.9), AM5, 294mm Pro, 7 filter wheel w/Antlia 36mm 3nm filters, ZWO EAF, Falcon 2 rotator, Giotto and Alto, Pegasus Power Box, Mele Quieter 3. I just got an EdgeHD 9.25 and getting that set up has been... a pain. I love the images though. Clear skies!
Wow, nice setup on your FRA400! Keep me posted on your EdgeHD 9.25. Seems like a potential upgrade to my EdgeHD 8 at some point down the road.
I've never used a rotator and use both of the cameras you mention. Logically, not sure why you would need a rotator on a wide field scope. Also, I shoot my calibration frames once per season because my field of view orientation does not change. This gives me a great result. If you had a rotator, you would need to shoot calibration frames each time you used the scope. Way too much work - at least for me.
Great points! I think the decision to purchase was a carryover from my days as a photographer where I was known to suffer from GAS (gear aquisition syndrome). 😉 I like to learn about new things and wanted the experience of using a rotator. That's why I had no hesitation to remove it. Thank you for taking a moment to drop a comment. Much appreciated. 👍
Hi Bill, just curious, are you only moving the Redcat down to Starfront?
I'm moving the RedCat and the EdgeHD 8 as well. Dropping both off at Starfront on December 29th. I expect it will take them a couple of weeks to put in place on the piers before I can remote intothem. I expect I will learn a lot! 😉
Oh awesome!
Let's talk calibration. Your light frame, i.e. the one you take under the stars of whatever target you're shooting, contains a number of unwanted things. Sensor noise. Optical defects. Dark current. Calibration removes those unwanted things. The darks remove additive things like dark current / amp glow. The flats remove multiplicative things like light falloff. But here's the thing - those flats are just lights, so they contain the same type of additive issues like dark current and amp glow. Just like you subtract a dark from a light, so too do you subtract a dark from a flat. Wait a second... so then what is this bias and why do people use them to calibrate a flat? Well, a bias is just an extremely short dark, typically taken at the shortest exposure your camera can do. For cameras like the 294 or 2600, that is 32 microseconds.
So why do people use a bias in lieu of a dark to calibrate a flat? Simple: it's convenient. Flats (which remember are just lights) are usually pretty short exposures. We're talking a few tenths of a second or less, especially if you're taking sky flats using our own sun as your light source. Because it is so short, there really isn't time for all of those additive things to have any real impact on the data. The only additive thing we really need to remove is the offset, which is precisely what the bias frame represents. Thus, calibrating a flat with a bias is "good enough". In most cases.
The sensor in the 294 is quirky. Whereas quite a few other cameras behave in a predictable, easily modeled linear fashion, the 294 doesn't at extremely short exposures. In fact, it's not until you've gotten to exposure times of around 2 to 3 seconds that the camera behaves properly. This means there's plenty of time for those nasty additive elements to play havoc, and thus you must take matching darks to subtract them all out.
Now, there are plenty of people who will swear up, down, left and center that they can take short flats and use biases with their 294. Maybe they got a good sample of the sensor. Maybe they're not getting the best calibration they can and deal with it during image processing. Maybe they just don't know. There are hundreds (perhaps even thousands) of pages of debate on the astrophotography fora about using darks or biases to calibrate flats. My stance on the matter is that using matching darks with your flats is the best way to calibrate, regardless of which sensor you're using. Having written that, with my Poseidon-M Pro (same IMX571 sensor in the 2600MM Pro), I use biases to calibrate my flats and don't even bother taking darks for my lights, instead using the same biases to calibrate them. The old adage do as I say, not as I do is certainly apropos :).
Love it! Thanks Jonny for your willingness to share your knowledge. Need to do an interview with you one of these days. 😉