The meade one is ok and has good speed control. Its a bit noisy and some come with a fair bit of backlash at times, but other wise they are ok for mid range focusers.
Don't expect wonders of automation from them though
The meade one is ok and has good speed control. Its a bit noisy and some come with a fair bit of backlash at times, but other wise they are ok for mid range focusers.
Don't expect wonders of automation from them though
What others would you suggest. I've looked at the Crayford 10:1 focuser as well.
You need to workout whether you want something in your optical path or out of path. What level of automation do you want - full automation can takes sometime to set up, but is really the most accurate for imaging (especially if you have filters which are not all parfocal - such as a Ha filter compared to a RGB set). You'll need a PC available for automation. Do you need temperature compensation, backlash compensation etc etc. For casual observing, just about anything will do the trick (well almost anything). You also need to ask how much budget you have. Focusers like the FLI PDI is expensive as it does not increase the backfocus much. Perhaps further research is required.
You need to workout whether you want something in your optical path or out of path. What level of automation do you want - full automation can takes sometime to set up, but is really the most accurate for imaging (especially if you have filters which are not all parfocal - such as a Ha filter compared to a RGB set). You'll need a PC available for automation. Do you need temperature compensation, backlash compensation etc etc. For casual observing, just about anything will do the trick (well almost anything). You also need to ask how much budget you have. Focusers like the FLI PDI is expensive as it does not increase the backfocus much. Perhaps further research is required.
I have to say that I hated mine (Meade) with a passion. It's incredibly fiddly to use from the handbox as you always have to remember what dang mode you're in - focus, slew, slew rate or somewhere else. A major PITA as far as I was concerned. I've chucked mine and will now use my William Optics 10:1 microfocusser - much better control, faster and with far less backlash. A beautiful unit indeed - if not a bit deep as it can potentially hit the bottom of the fork mount if you're not careful and have it carrying a camera or something longish. This is especially true if you're in polar mode rather than alt-az.
I have to say that I hated mine (Meade) with a passion. It's incredibly fiddly to use from the handbox as you always have to remember what dang mode you're in - focus, slew, slew rate or somewhere else. A major PITA as far as I was concerned. I've chucked mine and will now use my William Optics 10:1 microfocusser - much better control, faster and with far less backlash. A beautiful unit indeed - if not a bit deep as it can potentially hit the bottom of the fork mount if you're not careful and have it carrying a camera or something longish. This is especially true if you're in polar mode rather than alt-az (as you have to hit zenith with is rarer).
Cheers
Chris
I thought it would have been harder to hit the bottom of the forks if your in polar? Or am I mistaken?
Wella after much research I (think) I've settled on the William Optics - 2" Crayford SCT Two-Speed Focuser.
I have only one question. can anyone confirm if this screws into the back of the telescope, and the has the diagonal+eyepiece attached. i don't want to start drilling holes into my tube.
Wella after much research I (think) I've settled on the William Optics - 2" Crayford SCT Two-Speed Focuser.
I have only one question. can anyone confirm if this screws into the back of the telescope, and the has the diagonal+eyepiece attached. i don't want to start drilling holes into my tube.
Cheers.
Dmn excellent choice. I love mine...buttery smooth and the ability to rotate the focuser with negligible shift is fabbo.
I missed what type of scope you have. If it's a Meade SCT with the standard visual back you should be able to screw it straight on. What size did you have, as I can only speak for my 12"? A 2" star diagonal slips into the draw tube just like any other focuser.
Dmn excellent choice. I love mine...buttery smooth and the ability to rotate the focuser with negligible shift is fabbo.
I missed what type of scope you have. If it's a Meade SCT with the standard visual back you should be able to screw it straight on. What size did you have, as I can only speak for my 12"? A 2" star diagonal slips into the draw tube just like any other focuser.
Cheers
Chris
Yeah I should update my profile. I've got a Meade 8" LX90 SCT (GPS, LNT). I use 1.25" diags and eyepieces but it comes with a 2" to 1.25" convertor.
Do you know who sells them in Australia?
When you go near the zenith in polar does it bump into he bottom of the forks?
What are the advantages and dis-advantages of a manual focuser over a motor driven one? Can they be hooked up to a laptop for automation?
There are three levels: manual, motorised (no computer interface) and motorised automated (with computer interface - there are actually two additional levels of automated focusers – relative or absolute positioning but lets not confuse the situation for the time being).
To specifically answer your question (well partly); If we take a simplistic look, when focusing a telescope manually you need to wait for vibration/other movement to stop after you’ve moved the focuser. A motorised focuser allows you to rack the focuser in/out without touching the telescope. This is generally not a major issue, but something to note.
Of more importance is to be able to measure the movement of the focuser drawtube or sct knob turn. Without measurements, it is difficult to return to precise focus. This is not a problem for visual work, but I would consider very important for astrophotography. You need to be able to repeat the focus consistently through different filters etc. If you are out of focus by 50 microns or more the image can appear soft and lack detail. You can purchase both manual and motorised focusers with digital or analogue readers to assist you with the measurements.
Automated focusing obviously also performs measurements, but this is noted on a computer not a digital or analogue reader. These measurements are analysed by specific focusing software, along with star values such as brightness and FWHM (Full Width Half Maximum). The computer then understands what position the focuser drawtube or sct knob turns to reach the most optimal focus. The computer can also be told of the differences in temperature and how to correct for this to maintain precise focus as the ambient temperature drops. In addition you can also tell the computer that if a specific non-parfocal filter is used, shift the focus by x microns to reach focus. If you are serious about astrophotography, an automated focuser set up is a time saver and ensures you reach precise focuser ~95% of the time. Its never 100% because the computer is analysing a star in real time, thus seeing conditions and star saturation can significantly affect focusing precision. I usually focus on the mag 4 star nearly the object I’m going to image, then slew back to the object. I refocus every 30 minutes as I haven’t finalised the temperature compensation as yet – on the todo list.
There should be nothing stopping you getting a RoboFocus motor on your WO to make it automated. If you intend doing this, you may also want to lock down you SCT primary mirror to reduce image shifts.
Bump into the forks?.... not sure on the 8" LX90..... sorry
I do on mine, but only when you're slewing around all night to a million different places it'll be a problem. If you aim to slew somewhere and stay in that vicinity for a while (photography for instance) then all I do is simply remove the diagonal, slew past the fork base and then re-insert the diagonal for the next long while. No problem really. Some might consider it so though.
There are three levels: manual, motorised (no computer interface) and motorised automated (with computer interface - there are actually two additional levels of automated focusers – relative or absolute positioning but lets not confuse the situation for the time being).
To specifically answer your question (well partly); If we take a simplistic look, when focusing a telescope manually you need to wait for vibration/other movement to stop after you’ve moved the focuser. A motorised focuser allows you to rack the focuser in/out without touching the telescope. This is generally not a major issue, but something to note.
Of more importance is to be able to measure the movement of the focuser drawtube or sct knob turn. Without measurements, it is difficult to return to precise focus. This is not a problem for visual work, but I would consider very important for astrophotography. You need to be able to repeat the focus consistently through different filters etc. If you are out of focus by 50 microns or more the image can appear soft and lack detail. You can purchase both manual and motorised focusers with digital or analogue readers to assist you with the measurements.
Automated focusing obviously also performs measurements, but this is noted on a computer not a digital or analogue reader. These measurements are analysed by specific focusing software, along with star values such as brightness and FWHM (Full Width Half Maximum). The computer then understands what position the focuser drawtube or sct knob turns to reach the most optimal focus. The computer can also be told of the differences in temperature and how to correct for this to maintain precise focus as the ambient temperature drops. In addition you can also tell the computer that if a specific non-parfocal filter is used, shift the focus by x microns to reach focus. If you are serious about astrophotography, an automated focuser set up is a time saver and ensures you reach precise focuser ~95% of the time. Its never 100% because the computer is analysing a star in real time, thus seeing conditions and star saturation can significantly affect focusing precision. I usually focus on the mag 4 star nearly the object I’m going to image, then slew back to the object. I refocus every 30 minutes as I haven’t finalised the temperature compensation as yet – on the todo list.
There should be nothing stopping you getting a RoboFocus motor on your WO to make it automated. If you intend doing this, you may also want to lock down you SCT primary mirror to reduce image shifts.
Jase, that was a really helpful post. It's made everything so much clearer. Thank you
Bump into the forks?.... not sure on the 8" LX90..... sorry
I do on mine, but only when you're slewing around all night to a million different places it'll be a problem. If you aim to slew somewhere and stay in that vicinity for a while (photography for instance) then all I do is simply remove the diagonal, slew past the fork base and then re-insert the diagonal for the next long while. No problem really. Some might consider it so though.
I'll check them out. I can get it for USD200 but there's postage etc. I'll see which is the more economical and practical.
Thank you to all who contributed. Sorry if some fo the questions seemed a bit idiotic.
I'll check them out. I can get it for USD200 but there's postage etc. I'll see which is the more economical and practical.
Don't bother getting it from the USA IMHO. It's AU$299 here at Andrews, and US$200 is currently worth AU$236.35 - so you save AU$62 and still have to have it shipped. Plus, if you buy here, at least you get local support if you need help or replacement for any reason and have no warranty issue.
Don't bother getting it from the USA IMHO. It's AU$299 here at Andrews, and US$200 is currently worth AU$236.35 - so you save AU$62 and still have to have it shipped. Plus, if you buy here, at least you get local support if you need help or replacement for any reason and have no warranty issue.
Cheers
Chris
Omaroo, I can't quite tell from the photos I've seen on the web but are you able to mount a DSLR onto the focusser?
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