Teleconverters

I have just finished reading John Shaw's book -- Closeups in Nature.

It was a good book and I learned quite a bit about macro.... but it did leave me with one question.

If you loose 1 stop of light with a 1.4x and you loose 2 stops of light with a 2x.

Would it be safe to say that if you stack (2)1.4x then you will only loose 2 stops and thus have 2.8x with the same light loss as a standard 2x?

Kevin - Teleconverters don't add, they multiply. So two 1.4's would get you :

1.4 x 1.4 = 1.96

or approximately the same 2X with 2 stops light loss as the 2x converter. UNfortunately, there is no "free lunch" when it comes to optics like this. It's always a trade off.

Thank you David for setting me straight.

I knew it was too good to be true.

What got me to thinking about this is... .Yesterday I got in my Sigma 50/500 and a Sigma 1.4x tele. I put them both together and was shooting the moon last night and all the smaller craters were visiable. The Moon was full and pretty much straight overhead.... I had to lay on my back and balance the camera on my face to get the shots. I figured with a little more magnification I could prob also get nice closeups of the craters. The moon itself was almost full frame on a D80.

Crater close-ups would require quite a bit more reach than any teleconverter could supply with good IQ I think Kevin. I'm assuming that by the moon being "almost full-frame" you mean the circle of the moon barely fit inside the frame. If that's the case, you'd have to almost double your focal length just to get the moon to fill the frame with no black part of the frame showing. Add to that getting in close on a crater and I'd (total guess) that you'd need at least 3000mm. (Maybe someone who's tried this can chime in.) You were shooting at about 1050 mm last night.

I'm not sure how much cropping you're willing to do, but if you get a very sharp shot (which might be really difficult at these focal lengths) you could probably crop quite a bit too.

Here is the photo that I took last night.... I did NOT crop this in any way.

http://i101.photobucket.com/albums/m49/southernwolf/Nature%20Shots/Full-Moon--WEB.jpg

I once shot the moon with a 560 and 2x and the moon "dot" was about 5mm in diameter on a 35 mm frame. The optics were really excellent, however, and with the help of a solid tripod and mount and an electric release I was able to get a very sharp image of the moon about 7" in diameter on an 11X14 print now hanging on my den wall. Craters were sharp and the surface details quite discernable. This was before I got my digital rig but I imagine the numbers would play out about the same.

Looks pretty nice Kevin - good job. How does it look at 100%? These are really tough to get sharp. Even a good tripod doesn't always help. I love all the craters right along the shadow though.

Anyway, look at a crater you'd like a close-up of, and calculate how much of the frame that is. You can figure the focal length you'd need for a crater portrait. For instance, if the crater took up half the area of the frame (0.5), you'd need to double the focal length (1/0.5 = 2). If the crater was 1/10th (0.1) of the frame you'd need 10x the focal length (1/0.1 = 10). The focal lengths get very long, very quickly.

it doesnt look too bad (not great...but not too bad) at 100%.... but I would have rather had the camera on a tripod for more stability.... I may try it again when the moon isnt so high in the sky and I can use a tripod.... preferably when its orange in coloraton.