The greater the magnification the more exacting the use. Here are some tips that work well for me. Many supplied by dad who has actually ground telescope mirrors for a hobby.
1. Can't have too big or sturdy a tripod. C5 is approx 25X with camera. Tripod should settle down in 3 seconds are less when tapped lightly. Don't shoot off deck and don't move around while camera is shooting. Camera strap can't be flopping in the wind. Use quick release strap and remove it.
2. Vibration must be kept to a minimum. With K10/20D use 3 sec mirror lockup with wireless remote. Gotta love that rear mounted remote sensor.
3. Consider hanging weight from tripod to increase mass. This could be a milk jug full of water or a home made bean bag on top of lens. Also hanging the camera bag can help.
4. Make sure lens is clean optically. Remember clean in straight "spokes" from center to edge. Do not leave back of lens open to the elements! It is hollow. Dirt that enters rear can't be cleaned out without disassembling lens! Some people will put a high quality UV filter between back of lens and T adapter tube to "seal" the system to dust.
5. Lens shade is a must with large element lenses. You will increase contrast a lot. Also slows dew from forming for night time astronomy.
6. Be careful with lens. No shakes or bumps. It is possible to knock a mirror out of alignment. This can be adjusted by using the screws hidden under the front obstruction. This should not be done unless you know how. It is tedious and must be done while observing points of light (stars are great).
7. Old timers will focus the moving mirror all the way back for moving and storage. This parks it in a stronger position. Pia to me. Lots of turns to get back to normal focusing range.
8. Find that the Pentax magnifying eye cup helps with focus. Also use the Oly varimagni finder for higher mag.
9. C5 tube is solid - doesn't turn to focus. Uses a back knob that is like a caliper. So smooth. Since tube is solid, I often put a white sheet of typing paper around it to reduce day time heat. Also will make a camo one for skittish birds. C5 is strong enough (1250mm) that most animals don't mind you. C90 tube turns to focus so this tweak may not work as well if at all.
10. Long lenses are very much affected by temperature differences. It takes time for the lens to settle down and offer its sharpest performance. Carbon tubes help but the actual glass and mirrors also change and must have time to do so.
11. Atmosphere affects quality. You can see it "boiling" thru lens on a hot day. Shooting out of warm house into cool air or vice versa is bad. Shooting over asphalt or concrete is bad. Shooting over grass or water is good.
12. Check tripod mount where it attaches to lens. Have seen these get loose with time (especially C90 & C5). Can't have play in it. Don't go crazy and over tighten.
13. Put tripod as low to ground as semi-comfortable. It will shake less if you dont use extra leg extension or center column.
14. Shoot moon when it is higher overhead- less atmoshere. It will be sharper.
15. For moon shots set lens outside for an hour before shooting. Gives lens better chance to adjust to temperature. Will be sharper.
16. If tripod has spikes sink them hard into the ground. Ground helps absorb vibration.
17. If shooting jpeg set contrast higher in camera. Might also want to do sharpening - though I prefer to do that in computer.
18. If tripod doesn't have leg braces consider making some out of light chain. Just go from leg to leg. Can attackh with hose clamps. Not pretty.
19. Try to shoot decent shutter speed since we are moving. Wouldn't want less than 1/60 sec if possible. Would rather rise iso. Not over 800.
20. Recheck lens focus. It can change with time. Also use the zoom function on camera lcd to check focus of shots.
21. Adding a plate or brace between lens and camera body can help stop vibration or slop between them. Haven't found this a problem with C5 or larger mirrors. Seems to help C90 users.
22. For tripods that are still twitchy you can also mount a monopod to the camera body for extra stability. A little ingenuity could make it clamp to the tripod leg. Manfrotto makes a good clamp for this. This will slow down pointing the lens.
23. A finder scope is helpful for aiming the lens. When you get into the 1000mm range it is hard to figure out what you are pointed at. A finder scope that is properly aligned will speed up subject acquisition considerably.
24. A small battery powered blow dryer can be used to "clear" the inevitable dew that occurs at night when doing astronomical shots. Lens shade also helps.
Hope these tips help. Shooting high magnification takes time and practice.
Have fun with these long lenses.
thanks
barondla
Last edited by barondla; 06-17-2008 at 05:51 AM.