michael8554

T6 is M1.7 Michael

Me too ! I found a Canon 5D Repair Manual online, one of the sensor screws is M1.7 x 0.3, the other two aren't specified. But the 5D isn't a floating sensor model. Michael

Yes James, those figures show a reasonable range of pitches, shows that it will be important to measure the pitch when doing the mod. But my Merc has some bolts with Star heads, and the bolt diameter is one size bigger than the head ! Yes, Torx is 6 points, but there are 6 pointy "dips" in between the points, thats what Gary means by 12 points. I was slightly exaggerating when I suggested M12 ....... Michael

I agree that 0.147MM = 1/12th turn makes no sense to me, suggests the Torx screws have the same pitch as an M12 bolt you'd use on a suspension bridge. Now I've only read that the Torx Pitch is 0.5mm, but there's only a small range that's physically possible for such small screws -you'll have to measure. But there's Nagging Doubt that he knows something we don't know.... For a screw with 0.5mm pitch: 0.5mm = 1 turn = 12 points 1mm = 2 turns = 12/0.5 points = 24 points 0.147mm = 12/0.5 x 0.147 = 3.528 points - so where does his 1 point come from? A touch of Fake News to protect his Intellectual Property ? I've tackled Gary on his calculation, he wouldn't be drawn........ Michael

Latest is I have mounted an unmodded 450D on a 1280mm scope, and set focus on a barcode target. Then without altering the focus, tried the modded 450 at different offsets in the focuser of 0.10mm, 0.20mm, and 0.30mm, measured with feeler gauges. Best result was 0.20mm, not a million miles off the calculated value of 0.23mm. So I feel the formula using an RI of 1.545 (the average of Schott Band Pass Filter thicknesses) is looking suitable. But don't rush off modding until I've modded the other 450D, using feeler gauge material to give me new thinner shims under the sensor, and report back ! If that works out I'll try a 600D with the calculation for the "points" Michael

I showed my calculations to derive 0.17mm is 4.08/12ths of a turn, but the whole point of this post is for people to chip in with corrections to my calculations. So how do you get 1/12th turn is 0.17mm ? Michael

Hi Croz You can't hope they're the same thickness, you have to measure or you may end up with wrong Autofocus. You've seen that 450D filters could be 0.60mm or 0.65mm. And I hope you're thinking of removing LPF-2, not 1........ What bugs me is that Gary Honis and I are using the same formula to work out the correction, but are so different in our figures for Torx turns. I'll sleep on it and have a fix in the morning.....yeah right! Michael

Did a trial measurement this afternoon. Easy to say, impossible to do I'm afraid. Michael

Isn't it amazing how your brain works out problems while you're sleeping ? Attach modded 450D (autofocus wrong) camera to ota, critically focus with LiveView and Bahtinov mask. Attach unmodded 450D, critically focus by moving out of focuser tube, trickey so repeat, measure the gap each time between end of focuser tube and T ring with feeler gauges. This will give the figure the modded camera's sensor has to be moved inwards. That figure is only correct for that particular filter thickness, but does allow me to work out the correct RI of Canon's filters, which can be applied to any camera once the thickness is measured. It also tests wether the "move 0.20mm" statement is correct or not. Watch this space..... Michael

That's right, the Torx screws have to be tightened, to move the sensor closer to the lens. I have no problem with the professionals keeping their secrets. However, few owners have the nerve to mod, so discovering the right setting isn't going to be a world changer. Michael

That's only a third of a turn, if the Mod companies can do it, so can we....! Michael

I have just ploughed through the Schott Filters catalogue, the RI of their bandpass filters is between 1.54 and 1.55. So I discard the 1.43 figure above. I have another 450D I can mod, I will try making replacement thinner shims for this from feeler gauge material, based on a RI of 1.545, and report back. Michael

Thanks for clarifying Merlin. Michael

I agree with Gary's calculation in Cloudy Nights, except all the 450D LPF-2 filters I have removed are 0.65mm thick, not 0.60. Now one of the mod services says "0.21mm to compensate for removal of 0.7mm". 0.7mm is Gary's figure for the RETAINED filter thickness, not the difference of 0.6mm But taking 0.7 as correct, 0.21mm suggests a RI of 1.43, not 1.517. Somebody's got it wrong, not sure who..... Merlin, from memory only I thought we'd established your images did not look to be autofocused correctly with the clear clip in ? Michael

Ah, the ally Megawedge is much better than the standard one, plus the nylon washers. Set Dec Backlash on the scope to zero. Counter-intuitive but having a value confuses PHD2. Print out a list of the Autostar "Named Stars" and their numbers. Then pick the nearest one to your target, centre and SYNCH, focus, then GoTo your target, which will be spot-on. The quick way to GoTo a named star is: Press the "9 NGC" button Input the star number eg 032 and ENTER Now press the "6 Star" button Press ENTER Shows Star Named XXXXX ENTER GOTO Saves scrolling through the stars in their alphabetical order Michael

Yes Tris, the standard wedge is a POS. Tightening usually changes the alignment because the wedge bends so easily, so you have to learn to under adjust so that tightening gets you on the mark. Pier mounted and well drift aligned, I have never bothered with 1 or 2 Star alignments, I just SYNCH on a star near the DSO. Michael

My previous camera was a 500d. I too had it modded by Juan, because of the floating sensor. But my current camera is a 6D that nobody wants to modify, only to sell ready modded. I've already modded one high shutter count 6D, but I now want to do a newer one. The Autofocus is actually no big deal for my solely telescope needs, but would be a bonus in any future sale. Michael

I believe that Canon DSLR models starting with the 500D now have floating spring-loaded imaging sensors, adjusted by Torx headed screws. Here are my (untried) calculations for adjusting the sensor to preserve Autofocus after LPF Filter removal. Gary Honis gives superb instructions for modding almost every Canon DSLR at http://dslrmodifications.com/ Each LPF filter refracts the light passing through it, which extends the light path. So without a LPF filter the sensor has to be screwed in further towards the shutter to meet the autofocused image. Gary's calculation for the correction figure is based on a Refractive Index of 1.517 for the LPF: (0.517 x Thickness of Removed Filter) ÷ 1.517 = Correction in mm I understand the LPF#2 filter on the floating sensor models are 0.5mm thick, but that can be checked with a micrometer. **** MY 600D / T3i WAS ACTUALLY 0.60mm THICK ***** So for a LPF#2 removal, retaining the LPF#1 filter, the correction figure is: 0.517 x 0.50 ÷ 1.517 = 0.17mm EDIT *** READ MY FINAL POST **** I also understand the Torx T7 screws are M1.6 x 0.5mm pitch. To check, measure the length of 10 threads with a micrometer and divide by 10 to give the pitch. 0.5mm pitch means each full turn moves the screw 0.5mm in or out. Gary's method of adjustment uses "points". He notes that the star-shaped sockets of Torx screws have 12 "points". So before unscrewing the Torx screws he makes a radial Sharpie mark on each Torx screw head and the sensor mount. So on replacement, the Torx screws should be returned to the Factory "height", at which point the Sharpie marks should align. The final adjustment for 0.17mm Autofocus Correction is: EDIT ( ****** READ MY FINAL POST ***** ) 12 (points) ÷ 0.5 (pitch) x 0.17mm = 4.08 "points" (4.08/12ths of a turn). EDIT ***** READ MY FINAL POST ***** So the Torx screws are tightened a further 4 "points" to preserve Autofocus. EDIT **** FINALLY TIGHTENED 6 POINTS ****** I hope someone can confirm or refute these calculations before I get going on a mod !! Michael

Hi Tris Have you read the Instruction Manual ? Page 52 "Lining Up with the Celestrial Pole" Yes, the scope starts upside down ! Basically, you set the mount to Dec 90 on the setting circle, and align two tick marks on the RA axis. The scope is then roughly pointing at the NCP. It then rotates in RA and 14' in Dec to where it thinks Polaris is at that time of night. Centre Polaris with the wedge controls. The mount is now Polar Aligned. The problem is that during this alignment the scope in a very awkward position for observing Polaris! If you're on a permanent pier I would suggest: Go through the above as best you can, if necessary just assume Polaris is centred. Then Drift Align, which will give you a good Polar Alignment. Then GoTo a known star, Centre with the handbox, and SYNCH (hold ENTER down for 2 secs) Then "Park" the scope and switch off. You can enter a Custom Park position if you like. Next time you switch on you will already be Polar Aligned, maybe SYNCH again on a known star to check the sky map is good. You should also "Train Drives" which helps GoTo accuracy. Michael

Thanks guys, very usefull. Asus ZenPad 10 Michael

I think this covers it:

Why? Aren't all the sites recording the narrow band now instead of the nearest colour one? Michael

I have an earlier Pulsar, when the slit is pointing north, opposite to the south-facing door, the slit rail brackets prevent the door from opening ! But I put up with that because there are so many advantages to having a dome. Michael

Thanks Dave/ Are you the Dave in the link? I use Grabber to focus a DSLR in LiveView mode, which gives a continuous output as focus is adjusted. However with a CCD, which takes a couple of secs to download even a short exposure, Grabber doesn't work too well. This mask-guide looks the business for measuring individual ccd frames. Michael

Good thought Louise, but I think there would be a hotspot on his Darks, which there doesn't appear to be. Nigel, have you been into the menus and turned off all the custom settings? Michael